01 - Preheat an outdoor grill or grill pan over medium-high heat until hot.
02 - In a small mixing 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 stand for 10 minutes to allow the flavors to absorb.
04 - Place eggplant slices on the hot 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 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. Scatter torn fresh basil and crumbled feta cheese over the top.
07 - Serve warm or at room temperature as a main dish or side.