1. Prepare a medium-high gas or charcoal grill fire. In a medium bowl, mix the olive oil, thyme, marjoram, lemon zest, red pepper flakes (optional), 1/4 teaspoon salt, and 1/8 teaspoon pepper.
2. Brush the tomato and eggplant slices with 1 tablespoon of the herb oil. Season with 1/4 teaspoon salt and a few grinds of pepper. Marinate the mozzarella in the remaining oil.
3. Grill the eggplant, flipping once, until nicely browned and tender, 2 to 3 minutes.
4. To serve, put a tomato slice on four plates. Top each with a slice of eggplant, then a slice of mozzarella. Repeat, ending with a tomato slice. Drizzle with any remaining oil and serve.
Serving Suggestions: Serve with an Arugula Salad with Pesto Vinaigrette.