Steps
1. Heat olive oil in a skillet over medium heat.
2. Add the chopped onions and sauté until they are translucent.
3. Add the ground beef to the skillet, season with salt and pepper, and cook until browned.
4. Toast the bread slices in another pan until golden brown.
5. Spread mayonnaise on one side of each toasted bread slice.
6. Layer the cooked beef and sautéed onions on one slice of bread.
7. Top with sliced cheddar cheese and place the other slice of bread on top, mayo side down.
8. Grill the sandwich in the skillet for 2-3 minutes on each side until the cheese is melted and the bread is crispy.
9. Slice in half and serve with optional lettuce or pickles.