Warm a large skillet over medium heat and melt a small pat of butter or add a little oil.
Soften the onion for 3 minutes, then stir in the garlic and cook 30 seconds until fragrant.
Add the ground beef and cook, breaking it up, until browned and no pink remains. Drain excess fat if needed.
Season with salt, pepper, and Worcestershire. Stir in ketchup and mustard and simmer 1–2 minutes to thicken. Fold in pickles off heat.
Heat a clean skillet over medium. Lightly butter one side of a tortilla and place it buttered-side down in the skillet.
Scatter a layer of cheddar and mozzarella, spoon on beef mixture, then add a bit more cheese. Top with a second tortilla, buttered-side up.
Cook until golden and melty, about 2–3 minutes per side. Repeat with remaining tortillas and filling.
Rest 1 minute, slice into wedges, and serve with shredded lettuce and a drizzle of burger sauce.