Cut back the warmth to medium and add the remaining 2 tablespoons of the oil to the skillet. Add the squash and prepare dinner, stirring, for 1 minute. Add the water, cowl and prepare dinner till the squash is almost tender, about 4 minutes. Take away the lid, add the onion and prepare dinner, stirring, uncovered, till softened, about 2 minutes. Add the apple slices and prepare dinner, stirring, for 1 minute extra.