Slice the tofu into 1cm thick pieces.
Chop the onion, green onion, and Cheongyang chili pepper.
Add cooking oil to a pan and fry the tofu until golden brown on both sides.
Push the tofu to one side of the pan and stir-fry the onion and green onion.
Mix gochugaru (Korean chili flakes), soy sauce, sugar, minced garlic, and water to make the seasoning.
Pour the seasoning over the tofu and vegetables.
Simmer over medium-low heat until the sauce is reduced.
Add Cheongyang chili pepper and sesame oil to finish.