Arrange the sliced tomatoes in a large round baking dish and place the carp steaks on top.
Grind the onion, cilantro, parsley, garlic, lemon, and chili pepper together (save 1 tablespoon for the sauce). Combine all the rest of the gefilte fish ingredients in a bowl, and create oval patties to fit in the carp steaks. Place each patty inside the carp pieces, and spread the remaining mixture between the carp pieces.
Combine all the sauce ingredients in a bowl and spread it over the fish and patties. Add ½ cup of water to the sauce bowl, mix, and pour it around the fish. Sprinkle cilantro, lemon slices, and chili pepper, then cover.
Methods of cooking:
Baking: Bake for 40 minutes at 390°F (200°C) in the oven. Open the oven door and leave the dish inside for 10 minutes.
Stovetop: Cook over high heat for 10 minutes, reduce the heat to medium-low, and cook for another 25 minutes. Uncover and cook for 10 minutes to reduce the liquids.