Mince the onion and quarter the mini tomatoes. Remove stems from the tomatoes.

Combine mini tomatoes, ketchup, and a pinch of salt and pepper in a microwave-safe container. Cover loosely with plastic wrap and microwave at 600W for 1 minute. Stir to create the tomato sauce.

Mix ground chicken, minced onion, sake, salt, pepper, cornstarch, Parmesan cheese, and oregano in a bowl. Divide into 6 portions and shape into patties.

Heat olive oil in a frying pan over medium heat. Add the patties and cook until browned on one side. Flip and cover with a lid, cooking on low heat for 3–4 minutes until fully cooked.