Slice tofu into 1cm thick pieces.
Julienne onion and green onion.
Heat a pan with cooking oil and cook tofu until golden brown.
Drain oil from canned tuna using a strainer.
Place onions, green onions, and tuna on top of cooked tofu.
Make a sauce with soy sauce, red pepper flakes, minced garlic, sugar, and water.
Pour the sauce and water over tofu and simmer over medium-low heat.
Once the sauce has thickened and reduced, it's done.