In a skillet, fry potatoes in oil until tender, about 10-15 minutes. Place in the bottom of four individual 16-oz. Baking dishes. In the same skillet, scramble eggs in butter until set; spoon over potatoes. Top with ham. Pour 1/2 cup spaghetti sauce into each casserole; sprinkle with cheese. Bake at 350 for 20 minutes or until hot and bubbly.