Add the cilantro, onions and garlic to the bowl of your mini food processor. Pulse until finely chopped. Add in the mayonnaise, cheddar and spices. Continue to pulse until all the ingredients are incorporated. If aioli is still a little thick you can thin out with a splash of milk.
Cover and refrigerate until ready to use.
Place rack in the top most position of your oven. Slide a 12-inch cast iron skillet onto the rack and preheat your oven to 500 degrees.
Rinse the peppers under water and pat dry with a kitchen towel. Toss the peppers in a bowl with oil and kosher salt.
Once the oven and skillet are preheated, using own mitts, carefully remove the skillet to a heat safe trivet and add in the peppers. Place the skillet back into the oven, turn the oven to broil and cook for 1 to 2 minutes. Remove and stir with a wooden spoon and place back into the oven for another minute or two or until perfectly blistered.
Transfer to a platter, sprinkle with sea salt and serve with smoky white cheddar ailoi.