Preheat broiler to high.
Arrange bread on a rimmed baking sheet, coat with cooking spray.
Broil 2 minutes or until toasted, stirring once after 1 minute.
Heat a grill pan over medium-high heat.
Combine Salt, Pepper, Paprika, and Garlic Powder in a small bowl.
Rub spice mixture evenly over Steak.
Add Steak to pan, grill 5 minutes on each side for medium-rare or until desired degree of doneness.
Place Steak on cutting board. Let stand 5 minutes.
Cut across the grain into thin slices.
Combine Oil, Vinegar and Mustard in a large bowl, stirring with a whisk.
Add toasted bread cubes, Steak, Arugula, and Onion, toss to coat.
Divide salad among 4 plates.
Top evenly with Avocado and Blue Cheese.