In heavy 2-quart saucepan, melt 1/4 butter over medium heat. Stir in flour, salt, nutmeg and pepper. Cook and stir 1 minute; remove from heat. Gradually stir in milk. Cook over medium heat 5 to 7 minutes or until thickened and bubbly. Remove from heat; stir in lemon juice and cheese. Pour cheese sauce over squash mixture. Cover with foil.