Combine the tuna, chiles, red pepper, and green onion in a mixing bowl. Mix with a fork to break up the tuna. Add mayonnaise, mustard, and the lemon juice. Mix well. Taste and add salt and pepper if needed.

Lay out 4 slices of bread. Top each with the tuna mixture. Top the tuna mixture with grated cheese. Butter one side of each slice of bread and top the sandwiches with the bread, butter side up.

Heat a large griddle or skillet over medium heat. Place the sandwiches on the hot griddle, butter side down, and carefully butter the tops of the bread. Grill for about 3 minutes or until golden brown. Flip and grill for another 3 minutes or until golden brown and the cheese is melted.