Heat oven to 425ºF. Toss zucchini, onion, bell pepper and tomatoes with olive oil and salt and transfer to a rimmed baking sheet. Roast in oven, turning once, until vegetables are soft and golden, about 30 min.
Spread 4 slices toasted ciabatta with prepared olive tapenade and top with roasted vegetables. Serve warm or at room temperature.
Notes
Serve these open-faced sandwiches as lunch or dinner.