Preheat the oven to 350 degrees F (175 degrees C). Grease an 8x8-inch baking dish.
Lightly mix together ground beef, egg, bread cubes, onion, tomato, garlic, chili sauce, mustard, Worcestershire sauce, salt, and pepper in a bowl.
Wash peppers, and cut jack-o'-lantern faces into peppers with a sharp paring knife, making triangle eyes and noses, and pointy-teeth smiles. Slice off tops of peppers, and scoop out seeds and cores. Stuff peppers lightly with beef stuffing, and place them into the prepared baking dish so they lean against each other.
Bake in the preheated oven until peppers are tender and the stuffing is cooked through and juicy, about 1 hour.