01 - Preheat an outdoor grill or grill pan over medium-high heat until evenly hot.
02 - In a small bowl, whisk together the olive oil, balsamic vinegar, minced garlic, dried oregano, dried thyme, sea salt, and black pepper until well combined.
03 - Brush both sides of the eggplant and tomato slices generously with the marinade. Let them stand for 10 minutes to absorb the flavors.
04 - Place the eggplant slices on the grill and cook for 4 to 5 minutes per side until tender with distinct grill marks. Grill the red onion slices alongside if using.
05 - Grill the tomato slices for 2 to 3 minutes per side, just until lightly charred but still holding their shape.
06 - Arrange the grilled eggplant, tomatoes, and red onion in layered stacks on a serving platter. Sprinkle with torn fresh basil and crumbled feta cheese if desired.
07 - Serve warm or at room temperature as a main dish or side.