In a large skillet cook the bell peppers, onion, and garlic in the butter over mederately low heat, stirring, until the vegetables are softened. Stir in the crab meat, the lemon juice, the egg, the Worcestershire sauce, the mayonnaise, the mustard, and the cayenne, and divide the mixture among the muffin halves, mounding slightly. Sprinkle the sandwiches with Parmesan and broil under a preheated broiler about 10 cm from the heat for 3 to 4 minutes, or until the tops are just golden.