1In medium bowl, mix tuna, bell peppers, cheese and celery.
2Cut bread into four 4-inch pieces; cut each piece horizontally in half. For each sandwich, remove some of the bread from center of slices; discard bread or save for another use.
3Drizzle dressing on cut sides of bread; spread over bread. Fill each sandwich with 1/2 cup tuna mixture. Serve immediately, or wrap securely with plastic wrap and refrigerate up to 24 hours.