In a small saucepan combine wheat berries and 1-1/2 cups water; bring to boiling. Reduce heat. Simmer, covered, 30 minutes. Drain.
Lightly coat inside of 4- to 5-quart slow cooker with nonstick cooking spray. Place wheat berries, mushrooms, broth, rice, shallots, garlic, oregano, and 1/4 teaspoon each salt and black pepper in cooker. Cover; cook on low-heat setting 4 hours or until rice is tender.
Stir cheese and butter into rice. Turn off cooker. Let stand, covered, 15 minutes. Stir in additional broth if risotto is too dry.
Meanwhile, saute the 1 cup sliced mushrooms in a small amount of olive oil; set aside. To serve risotto, top with sweet pepper, sauteed mushrooms, and parsley. Makes 12 to 14 side-dish servings.