How to Make It
Combine chili powder, cumin, garlic powder, 1/4 teaspoon salt, and 1/8 teaspoon black pepper; rub evenly over both sides of steak.
Heat a grill pan over medium-high heat. Coat pan with cooking spray. Add steak to pan; cook 5 minutes. Turn steak over; cook 4 minutes or until desired degree of doneness. Place steak on a cutting board; let stand 5 minutes. Cut across grain into thin slices.
Combine vinegar, mustard, remaining 1/4 teaspoon salt, and remaining 1/8 teaspoon black pepper in a small bowl, stirring with a whisk. Gradually add oil, stirring with a whisk. Combine lettuce, cucumber, bell pepper, and shallots in a large bowl. Drizzle vinaigrette over salad; toss gently to coat. Top salad with steak and cheese.