Coat slow-cooker bowl with nonstick cooking spray. Place pork in bottom of slow cooker and toss with oregano, cumin, salt and pepper. Scatter onions, garlic and green peppers over pork, in that order. Pour salsa evenly over top.
Cover and cook on HIGH for 6 hours or LOW for 8 hours. Stir in cornmeal during last 15 minutes. Serve with rice and, if desired, top with sour cream and cilantro.
