1Separate cauliflower into florets. In 3-quart saucepan, heat 1 inch salted water (1/2 teaspoon salt to 1 cup water) to boiling. Add cauliflower, onion and lemon juice; cover and heat to boiling. Reduce heat; simmer about 6 minutes or until cauliflower is just tender. Drain.
2Heat oven to 425ºF. In ungreased 9-inch square pan, mix oil, garlic and parsley. Heat uncovered in oven 5 minutes. Spread cauliflower and onion in pan; sprinkle with pepper and cheeses.
3Bake uncovered about 20 minutes or until cheese is melted and forms a golden brown crust.