Cut the tofu and onion into bite-sized pieces.
Place the tofu in a pan and grill it on both sides until golden brown.
Move the grilled tofu to one side of the pan, add onion and tuna, and sauté.
Add soy sauce, chili powder, minced garlic, and water, and bring to a boil.
Return the tofu to the pan and simmer until it absorbs the seasoning.
Top with green onion and bring to a final boil to finish.