Preheat the oven to 180°c.
Rinse and dry the aubergines, cut them in half lengthways leaving the ends (or in three equal slices if using round ones) and remove the pulp from its skin with a spoon.
Peel and chop the onion roughly into pieces, add the crushed garlic in its skin and put in a saucepan over a medium heat with the rosemary oil. Brown the onion for 3-4 minutes and then add the aubergine pulp cut roughly into pieces.
Brown everything over a medium heat until the aubergine has completely softened.
Meanwhile, cut the feta into small to medium squares.
When the aubergine has cooled add the egg and the feta and mix well adding salt to taste.
Lay the aubergine skins on a baking sheet covered with parchment paper and fill them well with the pulp, drizzle over a little rosemary oil and cover with a layer of bread crumbs.
Bake for 20-25 minutes.
Serve the aubergines immediately and decorate as you like with chopped fresh cherry tomatoes, on a bed of rosemary sprigs lightly roasted in the oven or with chickpeas and olive oil.