Spread mustard over bottom half of muffins. Place in a greased 13x9-in. baking dish. Top with crab, lemon juice and zest. Sprinkle with cheddar cheese. Top with muffin tops; set aside., In a large bowl, whisk eggs, cream, milk, mayonnaise, salt, cayenne and pepper. Pour over muffins; sprinkle with Swiss cheese, Parmesan cheese, onions and peppers. Cover and refrigerate overnight., Remove from refrigerator 30 minutes before baking. Preheat oven to 375°. Cover and bake 30 minutes. Uncover; bake until set, 20-25 minutes longer. Let stand 5 minutes before serving. If desired, top with additional chopped green onions.