Prepare a large baking sheet by covering in aluminum foil. Spray foil with non-stick spray. Set aside.
Peel sweet potatoes if desired. I leave on the skins because I'm wild like that. Slice sweet potatoes 1/4 inch thick in any shape you wish.
Add sweet potatoes to prepared baking sheet.
Peel and slice onions in 1/4 inch half moons.
Drizzle enough olive oil over vegetables to coat. Sprinkle with 4-1-1 seasoning and chili powder. Toss to coat well. Arrange in a single layer.
Bake in preheated 400 degree oven for 45 minutes or until bottom side starts to brown.