Mix together tuna, ¾ cup mayonnaise, mustard, hot sauce and pepper, breaking up tuna as you mix
Add remaining ¼ cup of mayonnaise if you want the tuna creamier.
Evenly spread tuna mixture on 6 of the slices of bread.
Top with cheese slice and remaining 6 slices of bread
Preheat a skillet over medium heat
Butter outside of bread on each sandwich and place in heated skillet.
Grill sandwiches on both sides until bread is golden
Serve immediately.