Set oven rack 6 inches from heat and preheat broiler. Place English muffin halves on a baking sheet.
Coat skillet with cooking spray over medium-high heat. Cook sausage, onion, bell pepper, and mushrooms until sausage crumbles and veggies are tender, about 5 minutes. Drain and set aside.
Reduce heat to medium. Pour in eggs, season with salt and pepper. Scramble gently until set. Set aside.
Broil muffins until toasted, about 2 minutes. Top with sausage mix, eggs, cheese. Broil until cheese melts, about 3 minutes. Serve hot.
