Preheat the broiler on low. Line a baking sheet with aluminum foil, for easy clean-up.
Lay the English muffin halves and eggplant slices on the baking sheet. Drizzle the eggplant with olive oil and sprinkle with salt and pepper.
Broil for 3-5 minutes. Then flip the English muffin halves and eggplant slices over and broil for an additional 3-4 minutes, until the eggplant is tender. (If your bread is browning too much, you can remove it earlier.)
Remove from oven. Carefully stack an eggplant slice on top of each English muffin half. Top with a tomato slice and season with salt and pepper. Top each tomato slice with about ¼ cup mozzarella cheese.
Return to the oven and broil for 2-3 more minutes, until cheese is melted and slightly browned. Watch carefully so it doesn’t burn.
Serve as singles or stack as doubles.
Notes
You can easily double or triple the recipe to make an entire sheet pan of sandwiches if you are serving a crowd.
You could also spread the bread with pesto or drizzle some balsamic vinegar over top of these sandwiches for an extra flavor boost.