Preheat the oven to 425 degrees F. Preheat a grill for cooking on medium-high heat.
Drizzle the eggplants, zucchini and spring onions with 1/4 cup olive oil and season with salt and pepper. Place everything on the grill and cook until just seared, about 2 minutes per side. Place the bell peppers and tomatoes in a large baking dish. Bake until blistered, about 10 minutes. When cool enough to handle, dice all the vegetables and add to a medium (10- to 12-inch) cast-iron casserole dish. Set aside.
Add the garlic, pistachios and basil to a food processor. Turn on and drizzle in 2 ounces olive oil. Season with salt and pepper. Add 3 ounces olive oil and the cheese. Taste for seasoning and texture. Top the eggplant with the pesto and grate the Parmesan over the top.
Place the casserole in the oven and bake for 20 minutes.