Zucchini and red onions soak in a tangy marinade that cuts right through the richness of a barbecue feast.
In a large skillet, heat oil over medium-high. Add onion and saute until translucent, 3 minutes. Add vinegar and sugar and season with salt and pepper.
Transfer to a nonreactive bowl. Add zucchini and toss. Let marinate at room temperature 30 minutes.
To store, cover and refrigerate, up to 8 hours.