Start to finish: 40 minutes
1/4 cup extra-virgin olive oil
1 teaspoon Dijon mustard
1 teaspoon minced fresh rosemary
1 garlic clove, minced
Salt and pepper
6 portobello mushroom caps (4 to 5 inches in diameter), quartered
2 zucchinis, halved lengthwise and sliced 3/4 inch thick
2 red bell peppers, stemmed, seeded, and cut into 1 1/2-inch pieces
2 lemons, quartered
Whisk oil, mustard, rosemary, garlic, 1/2 teaspoon salt, and 1/4 teaspoon pepper together in large bowl. Transfer half of dressing to separate bowl and set aside for serving. Toss mushrooms, zucchini, and bell peppers with remaining dressing, then thread in alternating order onto eight 12-inch metal skewers.
— For a charcoal grill: Open bottom vent completely. Light large chimney starter half filled with charcoal briquettes (3 quarts). When top coals are partially covered with ash, pour evenly over grill. Set cooking grate in place, cover, and open lid vent completely. Heat grill until hot, about 5 minutes.
— For a gas grill: Turn all burners to high, cover, and heat grill until hot, about 15 minutes. Turn all burners to medium.
Clean and oil cooking grate. Place kebabs and lemons on grill. Cook (covered if using gas), turning as needed, until vegetables are tender and well browned, 16 to 18 minutes. Transfer kebabs and lemons to serving platter. Juice 2 lemon quarters into reserved dressing and whisk to combine. Pour dressing over kebabs and serve with remaining lemons.
Nutrition information per serving: 152 calories; 73 calories from fat; 8 g fat (1 g saturated; 0 g trans fats); 0 mg cholesterol; 332 mg sodium; 17 g carbohydrate; 5 g fiber; 10 g sugar; 6 g protein.