In a medium nonstick skillet, heat the oil over medium heat.
Chop onion and add to hot skillet; cook for 2 minutes, stirring once or twice.
Chop tomato and add to onion, cook for 1 minute more. Transfer the onion-tomato mixture to a bowl and set aside.
In a medium bowl, lightly beat together the eggs, egg whites, and water (optional). Pour the egg mixture into the skillet and cook over medium-low heat until they are almost set; stir frequently to scramble.
Drain any excess water from the tomato mixture, then stir gently into the eggs. Flavor with dill, salt, and pepper to taste.
Serve eggs with toast and bananas on the side.