Toast the sourdough bread slices with butter or olive oil until golden and crispy.
Season the pulled pork or flank steak with garlic powder, cumin, chili powder, salt, and pepper.
Cook the meat in a skillet over medium-high heat until heated through and slightly crispy on the edges.
Place slices of Swiss or pepper jack cheese over the hot meat and cover briefly to melt.
Sauté onions, bell peppers, and jalapeños in the skillet until soft and caramelized.
Mix mayonnaise, Dijon mustard, sriracha, lime juice, honey, and Worcestershire sauce to make the mule sauce.
Spread the mule sauce on the toasted bread slices.
Assemble the sandwich by layering the meat with melted cheese, sautéed vegetables, and optional avocado slices on the bread.
Press the sandwich in a panini press or skillet for a few minutes to meld flavors and crisp the bread further.
Serve immediately and enjoy your Mule El Cortez Sandwich!