Chop mushrooms, onion, cauliflower, and parsley into very small pieces. (Ideally, use a food processor to get them super small.)
Add the processed veggies to the ground beef and stir until well combined. Add the egg to act as a binder, and season with salt and pepper; mix thoroughly.
Shape into 4 patties; depending on the size, you may be able to make more. (If your burgers won't hold together, consider adding 1 cup of bread crumbs or oats!)
Spray a large skillet or griddle with cooking spray; heat over medium-high. Place patties onto skillet and cook 3-5 minutes per side until desired doneness is reached.
Serve on rolls with lettuce, sliced tomatoes, and other condiments as desired. Serve sliced bananas and strawberries on the side. (Serving size: 1 patty, 1 bun, 1/2 cup fruit)