Heat oven to 400°F. Grease 1 1/2-quart baking dish.
In medium skillet, melt butter over medium-high heat. Add onions; cook 5 to 6 minutes or until transparent.
In baking dish, stir together onions, beans, chili sauce, molasses and chili powder; mix well. Stir in SPAM® Classic; cover. Bake, stirring occasionally, 30 to 35 minutes or until hot and flavors are blended.