Divide 1 pound ground beef into eight equal balls, about 2 ounces each. Season with salt and pepper and prepare the toppings.
Heat a griddle or heavy skillet over medium-high heat. Smash each ball into a thin patty and cook for 2–3 minutes per side until browned and 160°F in the center; work in batches as needed.
Warm all eight taco shells according to the package. Soft shells can be warmed on the griddle for about 1 minute.
Place one patty in each shell and add about 2 tablespoons cheese. Divide the lettuce, tomato, onion, pickles, mustard, and ketchup among the eight tacos; serve two tacos per person.
Notes
Refrigerate promptly at 40°F or below; use within 2 days.
Reheat cooked leftovers to 165°F on the stove or in the microwave.
Keep shells, cooked patties, and cold toppings separate until serving.