Serves 6 to 8 (as a side)
2 large sweet onions, peeled and quartered
2 medium zucchini, cut lengthwise
2 yellow summer squash, cut lengthwise
2 large red peppers, halved and seeded
1 to 2 tablespoons olive oil
1 bunch green onions, trimmed
Kosher salt and freshly cracked black pepper, as needed
Mustard Vinaigrette Ingredients
¼ cup red wine vinegar
1 tablespoon Dijon mustard
1 tablespoon honey
½ teaspoon salt
1/8 teaspoon pepper
¼ cup canola oil
¼ cup olive oil
In a small bowl, whisk together the vinegar, mustard, honey, salt, and pepper. Gradually whisk in the oils until blended.
Preheat a grill to medium heat. Brush the vegetables with oil and season with salt and pepper. Add the onions to the grill first (total cook time of 15 to 20 minutes). About 5 minutes later, add the squash and peppers (total cook time of 10 to 15 minutes). Add the green onions last (total cook time of 2 to 4 minutes). Turn the vegetables as needed during cooking and remove from grill when lightly charred and crisp-tender.
Cut the grilled vegetables into bite-size pieces and combine in a large bowl. Add vinaigrette (about ½ cup or to taste) and toss to coat. Serve with remaining vinaigrette.