Season both sides of the sirloin well with steak seasoning and salt. Cook the steak on both sides to your desired temperature using a thermometer (see below). Once cooked, set aside to rest for 3-5 minutes before slicing thin against the grain.
Lay down the lettuce wedge, drizzle with dressing, top with tomatoes, blue cheese, and shaved onion. Season with salt and pepper. Serve with sliced steak.