Place trivet insert and 1 cup water in a 6-qt. electric pressure cooker., Cut and discard tops from peppers; remove seeds. In a large bowl, mix beans, cheese, salsa, onion, corn, rice, chili powder and cumin; spoon into peppers. Set peppers on trivet., Lock lid; close pressure-release valve. Adjust to pressure-cook on high for 5 minutes. Let pressure release naturally. If desired, serve with sour cream.