1 pound yellow squash and/or green zucchini
3/4 teaspoon salt
1/2 teaspoon black pepper
1/4 cup extra-virgin olive oil
2 tablespoons fresh lemon juice
2 teaspoons coarse-grain mustard
1/4 teaspoon sugar
Prepare grill for indirect-heat cooking over medium-hot charcoal. Trim squash and/or zucchini and halve lengthwise, then toss with salt, pepper, and 2 tablespoons oil in a large bowl. Oil grill rack, then grill vegetables directly over hottest part of coals, covered only if using a gas grill, turning over once, until grill marks appear, about 6 minutes total. Move vegetables to area of grill with no coals underneath and grill, covered, until tender, about 4 minutes more. Transfer to a platter. While vegetables are grilling, whisk together lemon juice, mustard, sugar, and remaining 2 tablespoons oil in a small bowl. Pour dressing evenly over vegetables before serving.