It's amazing what happens when you heat olives. 

We think of olives as a kind of garnish or as a no-effort hors d'oeuvres served cold, but they respond well to heat. It unlocks rich flavors that pair with zesty ingredients like the orange and chili in this recipe.

Passuluna means specifically Sicilian salt-cured black olives, which have a wrinkly appearance. You rinse the salt first, so if you cannot find true passuluna, good black olives (not those woody horrors in the cans) work out pretty well. 

Of course you can tone down the Sicilian heat by using just one or even no chilies, but this recipe is very good as written.