Cook the udon noodles according to package instructions. Drain and set aside.
Heat a pan or wok and stir-fry the tofu or chicken with soy sauce until browned.
Add the cabbage, mushrooms, and leftover peppers. Stir-fry for 3-4 minutes.
Mix in ponzu sauce and mirin. Add the cooked udon noodles and toss everything together.
Garnish with shichimi togarashi before serving.