Preheat oven to 400 °F.
Cut eggplants, bell peppers, and onions into 1″ cubes. Toss them in a large bowl with garlic, olive oil, salt, and pepper stir until well coated.
Spread them on a baking sheet make sure they do not overlap. Roast in oven for 45 minutes, until the vegetables are lightly browned and soft, tossing once during cooking. Cool slightly.
Place the vegetables in a food processor fitted with steel blade, add tomato paste and pulse 3-4 times to blend. Taste for more salt and pepper and season as needed.
This is very good on Garlic Toast or fresh Italian bread.