How To: Make filet mignon steak sandwich

Why put a steak on a plate when you could make it into an amazing sandwich? Betty shows you her special filet mignon steak sandwich recipe.

Ingredients: (for 2 sandwiches)

(2) filet mignon steaks, trimmed of fat and about a quarter-pound each (You may use any boneless steak you like.)
meat tenderizer, to taste (No MSG)
freshly ground black pepper, to taste
extra virgin olive oil, enough to spread completely over uncooked steaks
¼ cup mayonnaise
1 teaspoon prepared horseradish
1 medium onion, sliced into half-slices
About 8 portobello mushrooms, cleaned and sliced
2 tablespoons extra virgin olive oil for sautéing mushrooms and onions (1 tablespoon for each)
2 onion buns, split into halves, and toasted in an oven (cut side up)
fresh lettuce leaves