Rub oil on burger and season with a touch of salt and pepper.
Place the burger on a hot grill and cook on both sides evenly for 5 to 7 minutes.
Place 2 slices of onion on the grill until slightly charred.
Roll 2 lettuce leaves and slice thinly and mix with mayonnaise.
Place lettuce on a toasted bun along with tomato, and onions.
Top off with a grilled burger and serve.