Preheat oven to 350°F (175°C).

Slice tops from tomatoes and peppers and clean, saving the tops.

Remove pulp from tomatoes and reserve.

Place the saved tops in the baking dish and arrange the peppers and tomatoes on top to prevent burning.

Sprinkle 1/4 teaspoon of sugar into each pepper and tomato.

Heat 1/2 cup of butter in a large frying pan and sauté the finely chopped onion until transparent.

Add the ground lamb and stir until browned.

Add the parboiled rice, Greek mixed spice, and 1 cup of mashed tomato pulp.

Cover and cook for 15 minutes, then allow to cool.

Mix the Italian breadcrumbs into the meat mixture.

Fill the peppers and tomatoes with the meat mixture.

Place the remaining mashed tomato pulp on top of the stuffing.

Pour the tomato sauce into the baking dish and add enough water to bring the fluid level to 1/2 inch.

Bake in the preheated oven for 2 1/2 hours.

Check periodically to ensure the pan doesn't dry up; add more water if needed.