Combine broccoli, onions, and mushrooms in greased 10-inch microproof quiche dish or pie plate. Cover and cook on HIGH (maximum power) 5 minutes.
Blend eggs and half and half in medium bowl. Add rice, cheeses, salt, and pepper; stir. Pour mixture over vegetables; stir gently. Cook uncovered on MEDIUM (50% power) 9 to 11 minutes, or until quiche is set. Let stand 10 minutes.