Combine first 8 ingredients in medium bowl. Season to taste with salt and pepper. (Can be prepared 6 hours ahead. Cover and refrigerate.)
Preheat oven to 375F. Cut around stem of each bell pepper and remove, creating large opening at top. Scoop out seeds. Divide filling among peppers (about 1/2 cup each). Replace tops of peppers. Stand peppers in shallow casserole. Bake until filling is cooked through and peppers are tender, about 50 minutes. Serve immediately.