Coat a large non-stick skillet with cooking spray; place over medium-high heat. Add bacon; cook, turning once, until lightly browned, about 1 1/2 to 2 minutes. Remove bacon from skillet and place one piece on each English muffin bottom.
Off heat, coat same skillet with cooking spray; place over medium heat. In a bowl, beat whole eggs, egg whites, scallions, salt and pepper until blended; pour into skillet and scramble just until set and not dry, about 1 1/2 minutes.
Place 1/4 of eggs on top of bacon on each muffin bottom. Top each with 2 slices avocado and 2 slices tomato; cover with English muffin tops. Yields 1 sandwich per serving.