My aunt remembers my grandmother making these for the family during World War II when many food items were rationed. Good at any time of day–breakfast, lunch, dinner, or midnight snack!
Melt butter in a small skillet over medium-high heat. Saute the onion in butter until soft. Mash up the slice of luncheon meat with a fork, and add it to the skillet. Cook for 2 or 3 minutes, until browned. Pour the egg into the skillet so that it covers all of the meat and onion. Cook until firm, then flip to brown the other side.
Place the egg and meat onto one slice of the bread and top with cheese and tomato if desired. Place the other piece of bread on top. Bread can also be toasted first.
Per Serving: 558 calories; protein 22.6g; carbohydrates 30.4g; fat 38.7g; cholesterol 273mg; sodium 1499.8mg.