Step 1

Coat the bottom of a large skillet with olive oil and heat until shimmering. Season the eggplant slices with salt and pepper and cook over moderately high heat until golden, 6 to 7 minutes per side. Top each eggplant slice with a slice of cheese and cook until the cheese begins to melt, 1 to 2 minutes. Transfer to paper towels to drain. Wipe out the skillet and add more oil. Repeat with the remaining eggplant and cheese.

Step 2

Arrange the tomatoes and basil on the bottom halves of the focaccia and season with salt and pepper. Top with the eggplant slices and close the panini.

Step 3

Set a large cast-iron skillet or griddle over moderately high heat. Arrange the panini in the skillet and weight them down with a smaller pan. Cook the panini until the outside is crisp and the filling is heated through, 3 minutes per side. Cut the panini in half and serve at once.