Keto Philly Cheesesteak Pizza

Name: Keto Philly Cheesesteak Pizza
Ingredients: 1 pound sirloin steak; 2 tablespoons salted butter; 1 medium onion, thinly sliced; 0.5 teaspoon salt; 3 tablespoons vegetable oil, divided; 1 green bell pepper, sliced into thin strips; 8 ounces baby bella mushrooms, sliced; freshly cracked salt and pepper to taste; 1 pinch garlic powder, or to taste; 2 12-inch prepared keto pizza crusts; 0.5 cup sour cream; 2 teaspoons minced garlic; 0.25 cup shredded Parmesan cheese; 8 slices provolone cheese, cut into strips