Preheat an outdoor grill for medium-high heat and lightly oil the grate.
Season steak with garlic salt, black pepper, cumin, and cayenne pepper.
Grill on the preheated grill until medium-rare, about 5 minutes per side. Transfer steak to a cutting board and cover with foil.
Meanwhile, heat a large skillet over medium-high heat. Spread both halves of each roll with mayonnaise. Brown rolls, mayonnaise-side down, until golden, about 3 minutes.
Place refried beans in a microwave-safe bowl; microwave on high until warmed through, about 1 minute.
Slice sirloin steak against the grain into thin strips.
Spread a thin layer of beans on bottom half of each roll. Layer with steak, avocado, tomato, and lettuce. Top with cheese and top half of roll.
