Komatsuna and Tuna Mixed Rice (Japanese Mazegohan with Canned Tuna)

This is komatsuna and tuna mixed rice: finely chopped komatsuna greens and canned tuna, stir-fried for a couple of minutes in a sweet-sour soy seasoning, then folded into a bowl of hot rice. It’s a mazegohan — “mixed rice” — and it’s the kind of quick, thrifty dish Japanese families make on a busy night, or when there’s a bunch of greens in the fridge that needs using up.

That’s exactly how this one happened. I had half a bunch of komatsuna and a can of tuna in the cupboard, found a recipe on Cookpad, and followed it as written. It takes about ten minutes with rice that’s already cooked, and it’s a nice way to get a lot of greens into one bowl.

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The Short Answer

If you just want the method:

• What it is: Japanese mixed rice (mazegohan) with stir-fried komatsuna greens and canned tuna folded into cooked rice.
• The seasoning: for 2 bowls, 1 tbsp soy sauce, 1 tsp vinegar, and 1 tsp sugar, cooked into the greens until the liquid is gone.
• The method: fry the tuna in its own oil, add finely chopped komatsuna and sugar, then the soy sauce and vinegar, and stir over high heat until dry. Mix into hot rice.
• Time: about 10 minutes with leftover rice. No rice cooker setting needed.

Why You’ll Love This Recipe

• Ten minutes, one pan. Use leftover or freshly cooked rice — nothing goes in the rice cooker.
• Pantry and fridge ingredients. A can of tuna, some greens, and three seasonings.
• Lots of greens, painlessly. Half a bunch of komatsuna disappears into two bowls of rice.
• Great for onigiri and bento. It’s tasty cold, too.

What is Komatsuna?

Komatsuna (小松菜) is a leafy green sometimes called Japanese mustard spinach, though it’s actually in the cabbage family, not related to spinach. It has tender, dark green leaves and crisp, juicy stems, with a mild flavor and none of the bitterness of spinach. In Japan it’s one of the most common everyday greens: in miso soup, stir-fries, ohitashi, and dishes like this one. Outside Japan, look for it at Asian grocery stores; bok choy or spinach can stand in.

Mazegohan vs. Takikomi Gohan

Japanese mixed rice comes in two styles. Takikomi gohan is cooked together with the ingredients in the rice cooker, like my Japanese mushroom rice. Mazegohan, like this recipe, is made by stirring cooked, seasoned ingredients into rice that’s already cooked — faster, and perfect for leftover rice.

Ingredients (Serves 2)

Ingredient	Amount	Notes
Cooked Japanese rice	2 large bowls	Hot, or leftover rice warmed up
Komatsuna	½ bunch	Finely chopped; or bok choy
Canned tuna in oil	1 can (about 70g)	Partly drained
Sugar	1 tsp
Vinegar	1 tsp	Rice or grain vinegar
Soy sauce	1 tbsp

Use tuna packed in oil if you can: the tuna is fried in its own oil, so there’s no need to add more. (If yours is packed in water, add a little vegetable oil to the pan.) Mine was a Japanese can of “light tuna,” which is skipjack packed in oil. For the seasoning, Japanese soy sauce does most of the work; my bottle is a sweet Kyushu soy sauce. Serve it with good Japanese short-grain rice, which holds together better than long-grain.

How to Make Komatsuna and Tuna Mixed Rice

Step 1: Chop the Komatsuna Finely

Wash the komatsuna, shake off the water, and chop it finely, about 5 mm (¼ inch) — stems and leaves both. Small pieces mix evenly into the rice. Partly drain the oil from the can of tuna, but don’t drain it completely.

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Step 2: Fry the Tuna

Heat a frying pan and add the tuna with its remaining oil. Break it up and fry it lightly for a minute.

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Step 3: Add the Komatsuna and Sugar

Add the komatsuna and the sugar, and stir-fry over high heat for 1–2 minutes, until the greens wilt and turn bright.

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Step 4: Season with Soy Sauce and Vinegar Until Dry

Add the vinegar and soy sauce and keep stirring over high heat until there’s no liquid left in the pan. Watch it closely at the end so it doesn’t scorch. Cooking off the liquid is what keeps the rice from turning soggy when you mix it in.

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Step 5: Mix into the Rice

Put the rice in a large bowl, add the komatsuna and tuna, and fold everything together until evenly mixed. Taste, and add a few drops of soy sauce if you’d like it saltier — the right amount depends on how much rice and greens you have.

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Tips and Variations

• Cook off all the liquid. Any leftover moisture in the pan makes the rice mushy.
• Other greens work. Bok choy, spinach, or daikon leaves all work the same way. Squeeze spinach well, as it releases more water.
• Add sesame. A sprinkle of toasted sesame seeds or a few drops of sesame oil at the end makes it more aromatic.
• Make onigiri. Shape it into rice balls while warm for a lunchbox.

What to Serve It With

• A bowl of miso soup for a quick lunch.
• A rolled omelette — tamagoyaki — for a bento-style meal.
• A simple main like ginger pork for a fuller dinner.

Storing

Keep leftovers covered in the fridge for up to 1 day, or freeze single portions wrapped in plastic wrap for up to 2 weeks. Reheat in the microwave with a sprinkle of water. Shaped into onigiri, it can be eaten at room temperature in a lunchbox the same day.

Frequently Asked Questions

What is komatsuna in English?

Komatsuna is sometimes called Japanese mustard spinach. It’s a leafy green in the cabbage family with a mild, slightly sweet taste, and despite the name it isn’t a type of spinach.

What can I use instead of komatsuna?

Bok choy is the closest substitute. Spinach works too, but squeeze out its water after stir-frying so the rice stays fluffy.

Can I use tuna packed in water?

Yes. Drain it and add about a teaspoon of vegetable or sesame oil to the pan before frying the tuna.