Preparation Steps

• Combine sliced flank steak with olive oil, lime juice, cumin, minced garlic, salt, and pepper in a bowl. Toss to coat and let sit for 10 minutes while you prep vegetables.
• Heat a large skillet over medium-high heat. Add the marinated steak in a single layer and cook 2 to 3 minutes per side until browned and cooked to your liking. Remove steak and set aside.
• In the same skillet, add a little additional oil if needed and sauté the sliced onion and bell pepper until softened and slightly caramelized, about 4 to 5 minutes.
• Return the sliced steak to the skillet with the peppers and onions, toss to combine and warm through. Stir in chopped cilantro if using, then remove from heat.
• Assemble each quesadilla by placing a tortilla in a clean skillet over medium heat. Sprinkle a layer of cheddar and Monterey Jack, add a portion of the steak mixture, then top with more cheese and a second tortilla.
• Cook each quesadilla 2 to 3 minutes per side, pressing gently with a spatula, until golden brown and the cheese is melted. Add butter to the skillet between batches if desired for extra browning.
• Transfer to a cutting board, slice into wedges, and serve hot with sour cream, salsa, and lime wedges.