Put steak cubes in a bowl and add the Cajun seasoning. Toss to combine. Preheat a medium nonstick skillet or grill pan, and spray with nonstick spray. Add the steak to the pan; cook and stir until steak is cooked through.
PREPARE THE DRESSING:
If you have a blender, add the dressing ingredients to the blender and process until smooth. Otherwise, just stir together in a bowl until well-combined.
ASSEMBLE THE SALAD:
Add the spinach to a large bowl. Add the black beans, bell pepper, avocado and cooked steak. Drizzle desired amount of dressing on top and toss. Dish out individual servings, and serve with additional dressing on the side- as well as freshly ground black pepper.