Combine all sauce ingredients in a bowl, stir until smooth, and chill in the fridge.
Heat a skillet over medium-high and cook the beef, breaking it up, until brown, about 5–7 minutes. Drain excess fat.
Season the beef with salt, black pepper, garlic powder, and Worcestershire sauce. Mix well and remove from heat.
Lay tortillas flat. Place 2 cheese slices on one half, top with beef, onions, pickles, and 2 more cheese slices. Fold into half-moons.
Heat a skillet with olive oil over medium-high. Fry quesadillas 2–3 minutes per side until golden and crisp, cooking in batches if needed.
Let cool 1 minute, slice into 2–3 pieces, and serve immediately with chilled sauce.