This year, we're flipping the script and marinating after grilling. Inspired by the technique called escabèche, where cooked fish and meat are preserved in an acidic mixture, we're cooking first, marinating second. In the case of squash, it produces maximum flavor without compromising char or texture. To ensure that the squash is crisp-tender, pull it off the grill as soon as it's picked up some grill marks and a paring knife easily slips through the flesh.
Ingredients (4 SERVINGS)½ cup plus 3 Tbsp. extra-virgin olive oil, plus more for grill1 garlic clove, finely grated¼ cup white wine vinegar4 medium summer squash and/or zucchini, cut lengthwise ¼" thick1 medium red onion, cut through root end into 8 wedges2 bay leavesKosher salt, freshly ground pepper8 oz. feta, crumbled into large pieces4 banana peppers from a jar, thinly sliced crosswiseGenerous pinch of crushed red pepper flakes
Prepare a grill for medium-high heat; lightly oil grate. Whisk garlic, vinegar, and ½ cup oil in small bowl to combine; set marinade aside.
Toss squash, onion, and bay leaves on a rimmed baking sheet with remaining 3 Tbsp. oil to coat; season generously with salt and black pepper.
Arrange squash and onion on grate. Grill squash, undisturbed, until grill marks appear, about 3 minutes. Turn over and grill on second side until tender and starting to release liquid, about 2 minutes. Transfer squash back to baking sheet. Grill onion, turning occasionally, until tender and charred around the edges, about 5 minutes. Transfer back to baking sheet.
Arrange squash, onion, bay leaves, and feta on a rimmed platter and pour reserved marinade over. Scatter banana peppers on top and sprinkle with red pepper flakes. Let sit at least 15 minutes and up to 1 hour before serving.