Pour 2 egg whites into a glass custard cup about 4¾ inches wide or small dish, to create a round shape. Cover top of custard cup with a microwave-safe plate and place in microwave. Be sure to cover tightly so egg whites don’t pop out while cooking. Cook for about 1 minute, until cooked through. Carefully remove cooked eggs by running a spoon over bottom of eggs to lift out of custard cup.
To cook bacon: Line a microwave-safe plate with paper towels. Place 1 slice of bacon on top. Cover with more paper towels. Cook in microwave 2-4 minutes until bacon is cooked and crispy, if desired. Break cooked bacon into 2 pieces.
In the meantime, toast English muffin and spread inside of both pieces with light butter or preserves if desired. This is optional.
Place eggs on inside of bottom half of English muffin. Top with 2 bacon pieces, tomato, and cheese. Place top piece of English muffin on top. Heat in microwave for about 20-30 seconds until cheese is melted.
Serve at once or prep in advance and just before serving, heat until cheese is melted.