Leftover zucchini may get mushy. The best way to improve the texture and remove excess moisture is to reheat it on the stovetop or in the oven. You can also microwave, but the texture will be softer. Stovetop: Heat oil in a large skillet over medium heat, add the zucchini, stir occasionally, and cook until slices are reheated. Oven: Preheat oven to 350 degrees F, arrange slices on an oiled or parchment paper-lined baking sheet, and bake for about 10-15 minutes. Microwave: Place the zucchini slices in a microwave-safe dish, cover, and microwave in 30-second increments until warmed throughout.