In a saucepan cook peas according to package directions.
Meanwhile in a medium saucepan cook onion in butter till tender but not brown.
Blend in the flour and 1/2 teaspoon salt.
Add cream and lemon peel.
Cook and stir till thickened and bubbly.
Add cheese; cook and stir till cheese is melted.
Do not boil.
Add to sauce; stir to coat.