For the sheet pan veggies & chickpeas, preheat oven to 400ºF (200ºC, or gas mark 6), and have ready two large baking sheets.
In a mixing bowl, place eggplant, asparagus & chickpeas, 1 teaspoon olive oil, 1/4 teaspoon salt, onion powder, and pinch of black pepper. Stir to evenly coat, then spread into a single layer on a third of one baking sheet.
Next, combine mushrooms, peppers, onion & radishes with tamari, parsley, pinch of salt, and pinch of pepper in the mixing bowl. Then, spread it out on the second baking sheet.
Place baking sheets in the oven, roasting for 20 minutes, then switch pan positions (no need to move veggies around), and roast another 20 minutes. While everything is roasting, make the sauce.
For the tahini sauce, mix yogurt, tahini, lemon juice, parsley, basil, and salt in a small bowl, until smooth. Refrigerate until ready to serve