In a small bowl, combine tuna, olive oil, garlic, wine vinegar, onions, capers, and mustard powder.
Spread roll halves or bread slices with mustard. Spread tuna mixture over mustard.
Top with tomato slices, egg slices, and basil leaves. Top with remaining roll halves or bread slices.
Transfer to individual serving plates to serve.
Makes 2 servings.
* When purchasing canned tuna, purchase the best grade, which is the "albacore white" tuna.
Tuna Supreme Sandwich Recipe: https://whatscookingamerica.net/sandwich/tunasupsand.htm