Preheat the oven to 400°F (200°C). Cut the red bell peppers and eggplant in half and place them on a baking tray. Drizzle with olive oil and roast for about 25-30 minutes, or until the skin is charred and the flesh is soft.
Once the vegetables are roasted, remove them from the oven and let them cool slightly. Peel the skins off the peppers and eggplant. In a food processor, combine the roasted vegetables, garlic cloves, vinegar, salt, and black pepper. Blend until smooth.
Transfer the blended mixture to a saucepan and cook over medium heat for about 20 minutes, stirring occasionally, until it thickens. Adjust seasoning if necessary.