Based on the classic Spanish tapas, this tortilla can be served hot as a brunch or lunch dish. It work just as well at room temperature as an appetizer. What is presented here was inspired by Joie Warner's "take a can of tuna."
Fill a medium saucepan filled with water to boil over medium-high heat. Add potatoes and cook for 5-6 minutes until the potatoes are firm but tender. Add asparagus and cook an additional minute. Remove pan from heat and drain the vegetables well and pat to dry.
Combine the eggs and egg whites until well beaten. If desired add the milk and mix some more.
Heat olive oil in a non-stick pan with a heat proof handle. Add the potatoes and asparagus and cook for 5 minutes. Add the tuna and tomato and cook another minute.
Pour the eggs over the contents of the hot pan. Season with salt and pepper. While the eggs are still very wet, gently lift the sides of the eggs so that the more liquid parts slips under. Sprinkle the scallion slices on top. Reduce the heat to medium low and cover and cook for 3-5 minutes until the top is set but still moist.
Preheat the broiler to high. Place omelet under broiler for 1 or 2 minutes.
Slice the omelet into wedges and serve with salad.