Trim the ends of the zucchini. Using a vegetable peeler (or a mandoline), make flat, wide ribbons and place in a large bowl. Add 4 tablespoons olive oil, and the juice of the lemon. Toss well. Add the chopped mint and the feta cheese. Season lightly with salt, mindful of the saltiness of the feta cheese. Toss well. Add more olive oil as necessary to create a good balance between the oil, lemon juice, and feta.