Season both sides of the steak well with steak seasoning, salt and pepper and set aside.
In a bowl, mix together the sour cream, lemon, and horseradish. Season with salt and pepper. Set aside.
Heat oil in a non-stick pan over medium-low heat. Cook the steak on both sides to the desired temperature using a thermometer (see below; For medium-well or well-done place the steak in the oven 350°F to cook more evenly so the outside does not burn or char). Once the steak is cooked to your liking, set aside on a cutting board to rest for 3-5 minutes before slicing thin against the grain.
Lightly toast the bread and spread the sauce inside both halves, layer with spring mix, tomatoes seasoned with salt and pepper, sliced steak, and blue cheese.
Cut in half and serve with chips and pickles.