Preheat oven to 400°F (200°C). Brush eggplant slices with olive oil, season with salt and pepper, and roast for 20 minutes until golden.
In a skillet, cook diced onion and garlic until soft. Add the ground meat and brown thoroughly.
Stir in tomatoes, tomato paste, cinnamon, oregano, and bay leaf. Let simmer uncovered for 20 minutes. Remove bay leaf.
For the béchamel, melt butter in a saucepan, stir in flour to make a roux, then whisk in the milk. Stir constantly until thickened.
Add nutmeg, remove from heat, and let it cool slightly before mixing in the beaten egg and cheese.
In a baking dish, layer half the roasted eggplant, followed by the meat mixture, and top with the rest of the eggplant.
Pour béchamel sauce evenly over the top. Bake for 35–40 minutes, or until the top is golden and bubbly.
Let it rest 10–15 minutes before slicing. Trust me, it’s worth the wait.