Mix the cooked fish, red chili powder, garam masala powder, salt and coriander leaves together. Heat 1 tablespoon of oil in a pan and fry this mixture for 5 minutes. Remove from heat and set aside. Cut a slice from top of each tomato. Scoop out the centers and reserve the pulp for some other dish. Then turn the hollowed tomatoes upside down on paper towel and drain. Take one tomato and stuff it 3/4th with the prepared fish mixture. Then keep the mashed potatoes on top of it to seal the opening. Sprinkle breadcrumbs over it. Repeat the same with all the tomatoes. Bake them for 10-15 minutes at 375°F until tops are golden brown and the tomatoes are soft. Serve hot.