Drain the canned mackerel and pat the tofu dry with paper towels.

Mince the green beans and carrot.

In a bowl, mix the mackerel, tofu, minced vegetables, potato starch, egg, and salt and pepper thoroughly.

Transfer the mixture to a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for 10 minutes.

In a separate bowl, mix ketchup and soy sauce to make the sauce.

Flip the loaf out of the container, slice into serving pieces.