Zucchini-eggplant caponata toasts

Caponata, a traditional savory sweet-sour condiment, is often made with eggplant, but there are also versions made with artichokes. Here, it's made with eggplant and summer squash. It improves in flavor if made a day or two in advance of serving, as part of an antipasto or spread on baguette toasts for an aperitivo.