Chop the onion and mince the garlic; set them aside.
Place the chicken breasts at the bottom of the crockpot.
In a mixing bowl, combine the cream of chicken soup, chicken broth, frozen mixed vegetables, chopped onion, minced garlic, dried thyme, dried parsley, salt, and pepper. Stir until well mixed.
Pour the vegetable mixture over the chicken in the crockpot, ensuring the chicken is well covered.
Cover the crockpot and cook on low for 6 hours, or until the chicken is tender and easily shreds with a fork.
Once the cooking time is complete, shred the chicken directly in the crockpot using two forks, and stir to combine.
Preheat your oven to 400°F (200°C).
Unroll the refrigerated pie crusts and fit one crust into a pie dish. Pour the crockpot mixture into the pie crust, spreading it evenly.
Cover with the second pie crust, sealing the edges. Make small slits on top for steam to escape, and brush the top with a beaten egg for a golden finish.
Place the pie in the preheated oven and bake for 25-30 minutes, or until the crust is golden brown.
Remove from oven and let cool slightly before serving.