01 - Preheat an outdoor grill or grill pan to medium-high heat, approximately 400°F.
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 - Using a basting brush, coat both sides of each eggplant and tomato slice evenly with the marinade. Allow the vegetables to rest for 10 minutes so the flavors penetrate.
04 - Arrange the eggplant slices on the hot grill. Cook for 4 to 5 minutes per side until tender with visible grill marks. If using red onion, grill the slices alongside the eggplant.
05 - Place the tomato slices on the grill and cook 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 basil leaves and crumbled feta cheese over the top.
07 - Present the dish warm or at room temperature. Pairs well with grilled crusty bread, couscous, or quinoa.