Roasted Kielbasa & Vegetables Recipe

3 medium sweet potatoes, peeled and cut into 1-inch pieces 1 large sweet onion, cut into 1-inch pieces 4 medium carrots, cut into 1-inch pieces 2 tablespoons olive oil 1 pound smoked kielbasa or Polish sausage, halved and cut into 1-inch pieces 1 medium yellow summer squash, cut into 1-inch pieces 1 medium zucchini, cut into 1-inch pieces 1/4 teaspoon salt 1/4 teaspoon pepper Dijon mustard, optional