Cook frozen protein burgers as directed on box.
Meanwhile, in small microwavable bowl, combine broccoli and 1/4 cup water; cover with microwavable plastic wrap. Microwave on High 2 to 3 minutes or until broccoli is crisp-tender. Drain.
Place toasted bread slices on ungreased cookie sheet; spread each with mustard. Place protein burgers on bread; top with tomato slices and broccoli. Arrange cheese slices on top of broccoli.
Broil 3 to 4 inches from heat 1 to 2 minutes or until cheese is melted.