Put the aubergine and garlic cloves (skin on) onto a baking tray and put into a preheated, medium-hot oven. Bake until you can just push a skewer through - it should be al dente, not mushy inside. Let them cool and chill until needed. (This step can be done well ahead).
When you’re ready to make the frittata, remove the skin of the aubergine, then slice the meat into 1 cm thick pieces. Push the garlic out of its skin and mash it with a fork.
Mix the garlic with a little olive oil, oregano and salt & pepper into a paste.
Grease a non-stick frying pan with olive oil.
Cover the base of the pan with the aubergine slices. Brush them with the garlic paste.
Whisk the eggs in a small bowl. Season with salt and pepper. Cut the tomatoes and olives in half.
Heat the pan over medium heat, then pour in the eggs. Cook for a couple of minutes, then arrange the tomato and olive halves on top.
Put the lid on, then after a minute, turn the heat down and cook until the top is no longer runny.
Turn the grill on and brown the top of the frittata for a minute or so.
Transfer the frittata to a large plate and slice it into wedges. Serve with mint or Greek basil leaves scattered on top. Alternatively let it cool completely and cut it into bite-sized squares.