01 - In a bowl, gently combine ground beef with salt and black pepper. Shape into 4 even patties.
02 - Preheat grill or skillet to medium-high heat. Cook patties 3 to 4 minutes per side until desired doneness. If using cheese, place a slice on each patty during the last minute and cover to melt.
03 - While patties cook, toast burger buns until golden brown.
04 - Mix mayonnaise, Dijon mustard, and lime juice in a small bowl. Spread evenly on cut sides of buns.
05 - On bottom buns, layer lettuce, tomato, and red onion. Add cooked beef patties, top with avocado slices, and finish with top buns. Add optional pickles, jalapeños, or sprouts as desired.
06 - Serve immediately while warm.