Preheat oven to 425 degrees. Brown the sausage, drain it on paper towels. Slice into bite-slice pieces. Place the Brussels Sprouts, potato, green beans, and onions in a bowl with the olive oil. Coat all of the veggies. Place the vegetables on a cookie sheet and bake for about 35-45 minutes or until the potatoes are tender. Add the sausage to cookie sheet filled with the vegetables the last 15 minutes of the baking time.