In a large skillet, melt ghee over medium heat. Add onions & Peppers. Season with salt & pepper. Cook until soft, between 5-8 minutes. Place in a bowl and cover with foil, set aside.
In the same skillet, add avocado oil. Add steak. Cook for 5 minutes or until steak is browned. Add the sauce mixture & bring toa simmer. Cook until the liquid is 95% absorbed, about 5-7 minutes.
Optional: butter the buns and toast under the broiler or in skillet.
Assemble sandwiches: If using mayo, spread a layer of mayo onto your bun. Place bottom buns on a baking sheet. Pile with steak & pepper mixture. Top with slice of provolone. Place under the broiler 1-2 minutes, or until cheese is melted. Remove from oven, add top of bun & enjoy.