Bring a pot of water to a boil. Carefully add the tomatoes to the water, and boil until the skin begins to split. Remove from the water, cool under cold running water, and peel off the skin.
Place tomatoes into a large skillet, and mash with a potato masher. Mix in the bell peppers, onion and garlic. Simmer over low heat for about 20 minutes, or until onions and peppers are tender. Season with salt and pepper to taste.