Mix extra virgin olive oil, vinegar, lemon juice, herbs, pepper flakes, and garlic to make marinade.
Toss squash and zucchini with the marinade. Let these vegetables sit for 30 minutes to 2 hours.
Preheat Vegetable Tray on STOK® Grill to medium heat, between 300°F- 350°F.
If using the STOK® Tower, click here for heating tips.
Once grill is heated, grill onions until each side is nicely charred. Place onions in a separate grill-safe dish with lid. Cover and place on warming rack (if equipped). Allow the onions to steam while cooking the remaining vegetables.
Add remaining vegetables to the Vegetable Tray and let cook 15-20 minutes, turning once or twice.
Remove and discard skins from onions. Remove vegetables from tray and add to onions. Toss together and season with salt and pepper.
Serve.
