One Pan Turkey 'n' Stuffing

1 cup biscuit mix
1 1/4 cups milk
3 eggs
1 teaspoon parsley flakes
1 teaspoon dried sage leaves or 3/4 teaspoon ground sage
1/2 teaspoon salt
1/2 teaspoon poultry seasoning
1/8 teaspoon pepper
2 cups cut-up cooked turkey
1 cup chopped celery
1/2 cup finely chopped onion

Heat oven to 400 degrees F.

Saut