1. Thread shallots through roots and stem ends onto 2 metal skewers. Using sharp knife, cut 1/4-inch slits, spaced 1/2 inch apart, in crosshatch pattern on non-gill side of mushrooms. Brush shallots and mushrooms evenly with 1/4 cup olive oil and season with 2 teaspoons kosher salt (or 1 teaspoon table salt) and pepper to taste.

2. Whisk remaining 2 tablespoons olive oil, garlic, lemon juice, mustard, rosemary, and 1/2 teaspoon kosher salt (or 1/4 teaspoon table salt) together in small bowl; set aside.

3. Grill vegetables over medium heat, turning once, until tender and caramelized, 16 to 18 minutes (move vegetables as needed to ensure even cooking). Transfer vegetables to platter; remove skewers from shallots and discard any charred outer layers. Rewhisk vinaigrette, pour over vegetables, and serve.

Serves 4 to 6