Allow the peas to thaw, then blot them with a paper towel to get as much moisture off them as possible. You can speed up thawing by covering the peas in warm water for a few minutes.
Place them in a bowl and add oil and garlic salt. Stir to coat evenly.
Spread them on a baking sheet lined with parchment paper or aluminum foil.
Bake in the oven for 30 minutes, then shake and stir them around to make sure they are cooking evenly.
You can try them at this point to see if they are crunchy enough for you. If they need more time return to the oven for increments of 15 minutes until they are nice and crunchy. I usually bake mine for 45 minutes total to get them crunchy enough.