In a saucepan, heat your oil and saute garlic for 1 minute, add in the chopped onions and saute until golden. Season with salt, pepper and crushed red pepper, set aside in a small bowl to cool.
In a bowl, combine lamb, cooled onions and lemon zest, season with salt & pepper.
Gently combine the mixture until incorporated (without over-mixing).
Form into large meatballs (5-6).
Season feta with salt & pepper, break it into chunks and work a chunk into the center of each "ball".
Seal the meatball back up, cover and refrigerate for 45 minutes or so. **(If you don't like Feta, you can skip this step).
In your saucepan, saute the sliced onions until golden brown, season with salt, pepper and red pepper flakes. Remove any leftover butter (if any) by pouring it out or blotting the onions a little dry, Allow them to cool a bit. Add the fig jam to them and store in a covered bowl or mason jar until ready to use.
Make tapenade (or use store-bought).
Combine tapenade and mayo, mix well.
Set aside in a small bowl until using.
Can be made ahead of time, covered and stored in the fridge.
When ready to cook the burgers, oil grill, heat it to high.
Gently shape your "balls" into burgers.
Grill the burgers for 12-15 minutes or to your preferred level of doneness. The feta filling will help the centers of the burgers to not overcook, so if you like your burger well, you will need to cook them longer. i suggest placing them on your upper grill rack to finish off, so the exterior doesn't get dry if so,
Assemble burgers and enjoy!