Rub tuna with 1 tablespoon olive oil, and sprinkle salt and pepper evenly on both sides of tuna.
Grill, covered with grill lid, over medium-high heat (350° to 400°) 5 minutes on each side or until tuna reaches desired degree of doneness.
Brush bread slices with remaining 1 tablespoon olive oil, and grill 1 minute on each side or until golden.
Flake tuna; combine with ground red pepper, if desired, and next 4 ingredients. Spread tuna mixture evenly on 1 side each of 4 bread slices; top with tomato and avocado slices. Cover with remaining 4 bread slices.