In a mixing bowl, combine shredded cheddar, Monterey Jack, and optional pepper jack. Add mayonnaise, Dijon mustard, garlic powder, onion powder, salt, and black pepper. Stir until blended and creamy.

Take a large flour tortilla and spread half of the cheese mixture evenly. Add any additional fillings if desired. Fold the sides in and roll from the bottom to create a burrito.

Heat a skillet over medium heat, add butter, and melt. Place burritos seam-side down into the skillet. Grill for 3-4 minutes until golden brown. Flip and grill until cheese is melty.

Remove from skillet, cool for a minute, slice diagonally, and serve warm, optionally with salsa or guacamole.