This dish has equal amounts of tuna and rice by weight, which, in my opinion, achieves the ideal ratio of protein to starch. Although some may compare this to fried rice, it is much lighter and has a very low fat level. Despite this, the meal is nevertheless filling and cozy like other rice dishes.
Add water to the rice in a large saucepan, then stir to let the rice settle. Over medium-high heat, bring to a simmer; do not stir. Simmer for another 15 minutes on low heat with the lid on.
Put the tuna in a large mixing bowl and mash it up with a fork or your hands while the rice is cooking. Add the red bell pepper, the jalapeno, the 1/4 cup of green onions, the rice vinegar, the lemon juice, the soy sauce, the Sriracha, and the sesame oil. With a fork, combine everything completely.
Turn off heat and let rice sit, covered, for 10 minutes.
Transfer the rice to the mixing bowl after fluffing it with a fork to separate the grains and break up any big clumps. With a spoon, thoroughly combine the ingredients until they are fully integrated. If necessary, taste and adjust the seasoning. Serve with red pepper flakes and a teaspoon of green onion on top and serve warm, at room temperature, or cold like a rice salad.