Stir mayonnaise, cheese, and seasoned salt together in a small bowl. Set aside.
Sprinkle both sides of steaks with salt, pepper, and garlic. Set aside for 15 minutes.
Meanwhile, in a large skillet, heat 1 tablespoon oil over medium high heat. Add onion rings. Cook each side for 4-5 minutes until edges blacken. Remove to paper towels to drain.
Add remaining tablespoon of oil to skillet. Add steaks to oil. Cook for 4-5 minutes per side or to desired doneness. Remove to cutting surface and let rest for 5 minutes.
Meanwhile, remove most of oil from skillet using paper towels. Heat skillet again to medium high heat. Place split sides of buns in skillet and cook for 1-2 minutes until toasted.
Spread buns with mayo. Immediately add a mozzarella slice to each bun bottom. Thinly slice steaks into 4-inch long slices and divide onto cheese slices. Cut onion rings in half and divide onto steak slices. Top each with 2 slices of tomato and 2 basil leaves. Add bun tops.