Preheat oven to 350°F. Coat a large baking dish with nonstick cooking spray.
Wash tomatoes and peppers. Cut a thin slice from the tops of each to make a cap. Scoop out pulp from tomatoes and chop, adding pulp to tomato sauce. Scoop out seeds from peppers and discard.
Blanch peppers in boiling water for 5 minutes and drain well.
Sprinkle insides of tomatoes with sugar. Place them upside down on paper towel to drain.
Saute onion in butter over medium heat until transparent. Add mushrooms and continue cooking a few minutes. Add lamb, salt and pepper, and garlic, stirring until juices are absorbed. Add mint, rice and 1 cup of tomato mixture (sauce and pulp). Cover and simmer 20 minutes.
Place peppers and tomatoes in baking dish and fill with meat mixture. Place tops on peppers and tomatoes.
Pour oil over all and sprinkle with breadcrumbs.
Mix water and remaining tomato mixture and pour around vegetables.