Preheat: Set your oven to broil.
Prepare: Brush the eggplant slices with olive oil on both sides and place them on a grill pan.
Cook: Place the pan in the oven and broil the eggplant slices for 5 minutes on each side or until tender and lightly browned.
Assemble: Spread a layer of spinach leaves on the bottom halves of the ciabatta buns. Top with eggplant slices, crumbled feta cheese, and minced garlic.
Serve: Add the top halves of the buns and serve the sandwiches warm.