Grilled Zucchini and Eggplant Casserole with Pistachio Pesto

Name: Grilled Zucchini and Eggplant Casserole with Pistachio Pesto
Ingredients: 4 lavender or white small eggplants, trimmed and sliced in half lengthwise; Four 6-inch zucchini, trimmed and sliced in half lengthwise; 2 spring onions, sliced in half; Extra-virgin olive oil, for cooking; Sea salt and freshly ground black pepper; 4 bell peppers, colors of your choosing; 4 heirloom tomatoes; 4 cloves garlic, peeled and smashed; 3 ounces shelled pistachios; 1 bunch fresh basil, leavesseparated; 2 ounces grated Parmesan, plus more for serving