One of the perpetual challenges of the Sabbath-observant Jewish cook is finding colorful and flavorful dishes to serve at Saturday lunch that don’t require tons of day-of prep work or any reheating.

Caponata is a traditional Sicilian vegetable dish of sauteed eggplant, tomato, onion, and celery, along with briny green olives and capers. Sweet-and-sour flavors in the dish come from sugar and ...