Peas, Bacon, and Swiss Shells

1 cup frozen green peas
10 oz medium pasta shells
2 1/2 cups milk
3 Tbsp all-purpose flour
2 tsp Dijon style mustard
1/2 tsp salt
1/8 tsp black pepper
3 oz sliced Swiss cheese
4 slices bacon, crisp-cooked, crumbled
1 Tbsp grated Parmesan cheese

Preheat oven to 325. Lightly grease a 12x8-inch baking pan, set aside.
Place peas in colander. Cook pasta according to directions, omitting salt. Drain over peas in colander; set aside.
Meanwhile, which together flour, milk, mustard, salt, and pepper in large skillet. Cook and stir over medium heat until thickened, about 5 minutes. Remove skillet from heat; add Swiss cheese and whisk until smooth.
Place peas and pasta in bottom of prepared pan. Pour sauce evenly over peas and pasta; top with crumbled bacon. Bake until heated through, about 22 minutes. Remove from oven. Sprinkle with Parmesan cheese; let stand 5 minutes before serving.