Chop celery, onion, carrots and potato (peeled) into small pieces that are all the same size. Add everything to a pot over medium heat with your olive oil, and saute until translucent and fragrant.
Push the vegetables to one side of the pot, add a little more oil if needed - and then add your "Chicken". Cook until slightly browned, mixing in with the vegetables and adding your herbs when almost finished.
Add in vegan butter, and once melted, your flour and stir to combine. Slowly add in the almond milk, 1 cup at a time, while bringing the mixture to a boil. Give the mixture a few minutes to thicken but adjust the flour / milk ratio until you get the gravy to be to your liking. Although - a thicker gravy works best here to hold up in the sandwich.
Add in your frozen peas, salt and pepper to taste, and allow to cook for about a minute until the peas are warmed through.
While that's cooking, toast your buns.
When ready to serve, add a healthy scoop of the pot pie mix.