Season the steak slices with salt and pepper.
Heat a skillet over medium-high heat and cook the steak until browned and cooked through, about 3-4 minutes per side. Remove from skillet and set aside.
In the same skillet, reduce heat to medium. Place a tortilla in the skillet, sprinkle a generous amount of cheese on top, then add some of the cooked steak.
Place another tortilla on top, pressing down gently. Cook until the bottom tortilla is golden and crispy, about 2 minutes.
Carefully flip the mulita and cook until the second tortilla is crispy and the cheese is melted, another 2 minutes.
Repeat with remaining tortillas, cheese, and steak.
Serve hot, optionally topped with mashed avocado, diced tomato, chopped cilantro, and diced jalapeno.