Position a rack in the center of the oven. Preheat the oven to 350°F.

Lightly oil a 4- to 5-cup loaf pan

Cook, stirring, until the onions are tender but not browned, 5 to 7 minutes

Thoroughly combine the mixture, then pat into the prepared pan. Bake until the center feels firm when pressed, about 35 minutes. Let stand for 10 minutes, then unmold from the pan if you wish. Serve hot.