Preheat broiler to high. Line a broiling pan with foil. Set oven rack about 8 inches from heat source.
Bring a large pot of water to a boil over high heat. Halve peppers through the stems; remove stems, if desired, and seeds. Cook peppers in boiling water until tender, about 15 minutes.
Warm 1 Tbsp. olive oil in a large skillet over medium-high heat. Add onion and cook, stirring, until softened, 3 to 5 minutes. Crumble meat over onion and cook, stirring, until meat is no longer pink, 5 minutes. Stir in tomatoes and cook until most liquid has boiled away, 5 minutes. Season with salt and pepper.
Using a slotted spoon, transfer peppers to a colander; run under cold water. Drain and spoon 1/2 cup meat mixture into each pepper half. Arrange on broiling pan; sprinkle with bread crumbs. Drizzle with remaining olive oil. Broil until lightly browned and heated through, 3 to 5 minutes. (Watch carefully and remove before burning.)