Preheat oven to 400F.
Cut off top of garlic head, and place on sheet of aluminum foil.
Drizzle with olive oil, and wrap in foil, sealing tightly.
Place in oven for 30 minutes.
When done, remove, and set aside.
Once you take garlic out of oven, prepare the aioli.
Empty yogurt into bowl.
Add finely chopped kalamata olives, lemon juice, press garlic clove, salt, pepper, and feta if using.
Open foil with garlic head in it.
You should be able to simply squeeze out the garlic from within the cloves, take 2 tablespoons worth and add it to yogurt bowl.
Mix everything together.
Taste and see if more salt/pepper is needed (or any other item).
Let chill in refrigerator for 30 minutes or so.
Serve!