Onions - Dice onions. (Can be done up to 5 days ahead)
Make dressing - Chop garlic. Combine garlic, mayonnaise, ketchup, pickle relish, lemon juice, and paprika. Season with some salt and pepper. (Can be done up to 5 days ahead)
Heat a large skillet with oil over medium-high heat. Add onions and ground beef and cook, breaking the beef apart until cooked through, 6 to 8 minutes. Add Worcestershire sauce, salt, and black pepper and cook for a minute more, until everything is evenly seasoned. Set the ground beef aside to cool slightly.
Assemble the salads with a base of lettuce topped with tomatoes, cheese, croutons, and ground beef. Top with thousand island dressing. Enjoy!