Preheat the oven to 350℉. In a large skillet, heat olive oil and saute the ham and onion over medium heat until onion is softened and the ham is lightly browned. In a large bowl, combine the remaining ingredients; stir in the ham mixture. Transfer to a greased 13x9-in. baking dish.
Bake, uncovered, until a knife inserted in the center comes out clean, 35 to 40 minutes. Let stand 10 minutes before cutting.