Cut the yellow bell pepper into bite-sized pieces and thinly slice the onion.

Heat olive oil, doubanjiang, grated garlic, and grated ginger in a pan over low heat. Once fragrant, add the onion and sauté until softened. Add the yellow bell pepper and stir-fry. Mix in sake, sugar, salt, and ketchup, then cook over medium heat.

Divide the mackerel and stir-fried mixture evenly into cocotte dishes. Top each with shredded pizza cheese. Bake in a toaster oven for about 5 minutes until golden brown.