Arrange pepper skin side up in broiler pan (in batches if necessary) and broil until blackened. Wrap in paper bag and let stand 10 minutes to steam. Peel and pat dry.

Mix olive oil, lemon juice and garlic in large bowl. Season with salt and pepper. Add peppers and marinate at least 30 minutes. (Can be prepared 1 day ahead. Cover and refrigerate. Bring to room temperature before continuing.)

Drain peppers, reserving marinade. Combine tuna, chopped parsley and capers in another bowl, breaking up tuna with a fork. Mix in enough reserved marinade to season to taste. Season with salt and pepper. Place 1 tablespoon tuna mixture on inside of each piece of pepper at one end. Roll up. Arrange seam side down on serving platter. Pour remaining marinade over rolls. (Can be prepared 6 hours ahead. Cover and refrigerate.) Garnish with parsley sprigs and olives before serving. 16 appetizer servings.