Scalloped Potatoes with Sausage and Peppers

2 tablespoons olive oil 1 lb bulk Italian sausage 2 onions , thinly sliced 1 large red bell pepper , seeded and cut into 1/3 inch strips 1 large green bell[...]

1/3 cup margarine 1/2 cup flour 1 teaspoon salt 1/2 teaspoon black pepper 2 1/4 cups milk 4 medium potatoes , sliced thin 1 medium sweet onion , sliced thin 2[...]