Potato Hash with Bell Peppers and Onions

olive oil 1 Tbsp. unsalted butter 4 large or 6 medium potatoes, peeled and cut into ½” cubes 1 onion, diced 1 red bell pepper, diced 2 tsp. fresh parsley, chopped 3 garlic cloves, minced Salt and pepper, to taste 1/4 cup freshly grated Parmesan cheese