In a small bowl, combine mayonnaise, lemon juice, cayenne pepper, grated cheese, and salt and pepper, to taste. Add crabmeat to mayonnaise mixture and stir to combine. Spread crabmeat mixture on bread. Cover with a second piece of bread. Melt butter in a medium skillet over medium heat. Add sandwich and brown for 2 minutes; flip and continue to brown for 2 to 3 more minutes. Repeat with second sandwich. Slice and serve.