Once the oil is hot, add the sausage and cook, breaking it up as you go, until it's browned. Remove it and sprinkle it evenly into the bottom of the prepared pan. Then add the diced sweet potatoes to the skillet. Let them saute for about 5 minutes, then add in the peppers and onions. Cook, stirring occasionally another 5 or so minutes until the potatoes are almost tender and the onions and peppers have softened. Then add the zucchini and cook just a few more minutes, until it's all tender.