Steps
1. Spread the mayonnaise and mustard evenly on one side each of the two slices of bread.
2. Layer the lettuce, tomato, onion, ham, and cheese on the bread slice with mayo and mustard.
3. Top with the other piece of bread.
4. Heat a large skillet over medium heat, and melt the butter.
5. Place the sandwich in the skillet and cook until lightly golden and cheese has melted, about 5 minutes per side.
6. Cut in half and serve.