Preheat the Grill: Fire up your grill to medium-high heat, aiming for about 400°F.
Prep the Eggplant: Slice the eggplant into ½-inch thick rounds. Arrange the slices in a single layer, sprinkle both sides generously with salt, and let them rest for 20–30 minutes to draw out excess moisture. Pat the eggplant dry with paper towels, then arrange them in a single layer on a baking sheet.
Prepare the Marinade: Combine the olive oil, balsamic vinegar, minced garlic, salt, and pepper directly in a bowl, whisking until well blended.
Marinate the Eggplant: Lay the eggplant slices in a shallow tray or dish, then pour the marinade evenly over them to coat both sides. Let them sit for 5 to 10 minutes, then transfer the slices to a platter, shaking off any excess marinade before grilling.
Grill the Eggplant: Arrange the eggplant slices directly on the hot grill grate and cook for 4 to 5 minutes until they are lightly golden brown. Flip them over with a spatula and grill for another 2 to 3 minutes until tender.
Assemble the Salad: On a large plate or serving platter, layer the warm grilled eggplant slices, heirloom tomato rounds, and mozzarella, finishing with basil leaves.
Season and Drizzle: Finish the salad with a drizzle of olive oil and balsamic vinegar, then sprinkle with a pinch of salt and pepper.