Wash and dry the zucchini. Cut lengthwise into slices 1/3-inch thick. Place the zucchini slices in a colander, sprinkle with salt and set aside to drain for 2 hours.
In a large saucepan, heat the olive oil over medium heat. Place the drained zucchini slices in the pan and cook gently until golden brown on both sides, about 3 minutes per side, being careful not to burn the slices. Set aside.
In another saucepan, bring the vinegar and sugar to a boil over high heat. Add a pinch of pepper flakes and a pinch of salt.
Place the zucchini slices flat in a shallow bowl, with the garlic slices, basil and parsley scattered throughout. Pour the vinegar over the zucchini slices and let marinate, covered, for at least 24 hours before serving.