Put the olives in a mixing bowl.
Cut the lemon in half. Set aside one half. Slice the other half into rings, then each slice into 6 wedges. Add these to the olives.
Finely slice the garlic, add these to the olives.
Season with salt & pepper, pour over the olive oil, and squeeze over the juice of the other half of the lemon.
If you’re using a chilli, cut off its base and put it in a small, sterilised jar.
Mix everything together gently, then transfer the mixture into the jar, then seal.
Marinate for at least 2 hours, preferably overnight in the fridge. Keep chilled after opening.