Coat four 6-ounce ramekins with nonstick cooking spray. Divide the tomatoes, mozzarella and basil between the ramekins.
In a large bowl, whisk together eggs, egg whites and water. Divide the mixture between the ramekins, pouring over the tomato mixture. Divide the salt and pepper between the 4 ramekins.
Place the ramekins on a baking sheet and place in the oven. Cook until the eggs are set, about 20 minutes.
Remove from the oven, transfer the ramekins to plates and serve immediately.
The night before, place the tomatoes and cheese in the ramekins, and prepare the egg mixture. Cover and chill the ramekins and the egg mixture. In the morning, add the basil to the tomato mixture and pour the egg mixture over top. Add the salt and pepper. Bake as directed.