Pre-heat the oven to 450 degrees. Place the peppers on a cookie sheet and roast until the skin of the peppers is blackened on all sides. Alternatively, you can roast the peppers over an open flame or on the grill. Turn the peppers throughout the process to get even browning. Once the peppers are soft and blackened, place the peppers in a zippy bag. The steam will enable the skins to come off easily after about 20 minutes. Once you remove the peppers, carefully cut the stem of and remove the seeds. Finely dice the peppers before adding to the cheese.
With a box grater, grate the cheeses and the onion. Place in a large bowl.
Add the mustard, the garlic, salt and pepper to the cheese and onion. Stir in the chopped peppers and mayonnaise and combine well.
Serve with veggies, crusty bread or crackers. Room temperature is best. Store in the refrigerator for up to 2 weeks.