Preheat oven at 420 F.
Unroll the pie crust and precisely fit it in an 11-inch tart pan. Poke the dough all over with a fork. Then put the pie in the fridge.
On a baking sheet with parchment paper, arrange the eggplant slices in a single layer. Brush each eggplant slice with olive oil, add salt and pepper. Cook for 10 min. Flip each eggplant slice and cook the other side for an additional 5 min.
Meanwhile, finely slice one medium onion. In a skillet, add some olive oil. When it is hot, add the onion, garlic, salt, pepper, and sprinkle some herb de Provence, Italian seasoning, thyme, or oregano. Let them cook slowly until completely soft but not brown. Add 2 tablespoon of marinara tomato sauce and mix well. Cook just 1-2 min. Set aside.
When the eggplant slices are cooked, immediately spread a spoonful of marinara sauce over every eggplant slice. Set aside. Lower the temperature of your oven at 400 F.
Remove your tart pan from the fridge. Sprinkle grated parmesan to your liking. Scatter the onions over the cheese. Spread the eggplant slices all over the tart (you can overlap the slices). Then add the drained sardines evenly (I delicately cut each sardine lengthwise).
Add more parmesan, sprinkle herb de Provence, Italian seasoning, thyme, or oregano. Lightly drizzle olive oil.
Cook for 20 - 25 minutes until the crust and cheese are lightly golden. Just before serving, you may add some finely cut basil.