To make the sauce: In a small high speed blender or a food processor, combine the avocado, pesto, 2 tbsp. of olive oil, garlic powder, onion powder, 1/2 tsp of salt and pepper.Blend until smooth. Add the third tablespoon of olive oil if the mixture seems too thick.
In a large mixing bowl, combine the potatoes, celery, pepper, onions and the sauce mixture.
Gently toss until the sauce evenly coats the rest of the ingredients.
Taste for seasoning and add more salt if needed.
Chill for an hour.
Serve and enjoy!
** I would not recommend making this salad too far in advance since, as we all know, avocados like to turn brown. It would still taste wonderful but the appearance wouldn't be the most appealing. I like to make it only a few hours before I am ready to serve.