Cut eggplant in half lengthwise. Place eggplant halves, skin sides up, in a foil-lined baking pan. Quarter sweet pepper; remove stems, seeds, and membranes. Place sweet pepper pieces, skin sides up, in the baking pan.
Cut 1/2 inch off the pointed top of the garlic bulb. Remove the outer papery layers. Place garlic bulb on a square piece of foil. Bring edges of foil together to form a pouch; seal. Put garlic pouch in the baking pan.
Roast eggplant, sweet pepper, and garlic in a 425 degree F oven for 25 to 30 minutes or until eggplant is softened, pepper skins are blistered and dark, and garlic is soft. Wrap eggplant and pepper pieces in the foil, and let stand 15 minutes.
Remove pulp from eggplant pieces with a spoon and place in a food processor bowl or blender container; discard skin. Peel skin from pepper pieces with a sharp knife and place peppers in food processor bowl; discard skin. Press garlic pulp from each clove with your fingers and place in food processor bowl; discard skin. Add the snipped oregano, chipotle pepper, vinegar, oil, salt, and pepper. Cover and process or blend until almost smooth.
To serve immediately, transfer to a serving bowl; top with oregano sprig. Or, place in an airtight container and chill in the refrigerator up to 2 days. Stir before serving. Garnish with oregano sprig. Serve with assorted breads, crackers, and cold sliced meats. Makes 20 servings.