Prepare a charcoal fire using about 6 pounds of charcoal briquettes; let burn until the coals are completely covered with a thin coating of light gray ash, 20 to 30 minutes. Spread the coals evenly over the grill bottom; place grate on grill, and heat until hot. (It is hot when you can hold your hand 5 inches above the grill surface for no longer than 3 or 4 seconds.) Or, preheat a gas grill to high (450°F to 550°F). Or, lightly grease a grill pan, and place over medium-high until hot, about 2 minutes.

Meanwhile, combine tomatoes; sherry vinegar; garlic; 4 tablespoons of the oil; and, if desired, sherry in a medium bowl. Let stand 15 minutes.

Brush both sides of zucchini slices with remaining 1 tablespoon oil; sprinkle evenly with salt and pepper. Arrange zucchini slices on grill grate or in grill pan, and grill, uncovered, until charred and just tender, 3 to 5 minutes per side. Remove grilled zucchini to a platter, and cover with aluminum foil to keep warm. (The foil will also trap steam and result in delicious zucchini juices.)

Just before serving, chop or tear mint leaves from sprigs, and add to tomato mixture. (If you chop mint too far ahead, it will turn black.) Stir to combine; add salt and pepper, if needed, and immediately pour tomato salad and juices over warm zucchini. Garnish, if desired, and serve immediately with crusty bread to sop up the juices.