1Heat oil in a skillet over medium heat; cook and stir onion until tender and lightly browned, 10 to 15 minutes.
2Preheat oven to 400 degrees F (200 degrees C). Place pizza crust on a baking sheet or pizza stone.
3Mix sour cream and horseradish together in a bowl; spread onto pizza crust. Layer potato slices over sour cream; top with 1 cup Swiss cheese. Layer onion, prime rib, mushrooms, and green bell pepper on top; cover with remaining 1 cup Swiss cheese.
4Bake in the preheated oven until cheese is melted and crust is lightly browned, about 20 minutes.
Use any variety of cheese (such as mozzarella or provolone) in place of the Swiss, if desired.
1 tablespoon olive oil
1 onion, sliced
1 prepared pizza crust
1 cup sour cream
1 tablespoon prepared horseradish
2 baked potatoes, sliced
2 cups shredded Swiss cheese, divided
1 (3 ounce) fillet cooked prime rib, cut into bite-size pieces, or to taste