Preheat the oven broiler on low. Toss the tomato, onion, and garlic with olive oil on a foil lined baking sheet. Season well with salt and pepper. Place under the broiler until the tomatoes are soft and garlic is golden brown.
Place all ingredients (minus the jalepeno) into a blender or food processor and blend until smooth. Refrigerate in a shallow bowl or container until cool. Season with salt and pepper to taste before serving. Garnish with basil and jalapeno (if using).