Preheat the oven to 425℉.
Heat a large pan over medium high heat. Add in 1 tablespoon of the vegetable oil. Place the marinated chicken into the pan and let it cook for about 4-6 minutes on each side until seared to a golden brown color. Once the chicken is seared and cooked, remove it from the pan and set aside.
In the same pan, add in the remaining tablespoon of vegetable oil and the unsalted butter. Reduce the heat to medium. Once the butter has melted, add in the kashmiri chili powder, ground cumin, and garam masala. Let the spices toast for about 30 seconds then add in the onion, carrot, serrano pepper, garlic, and ginger. Sauté for about 5 minutes until the carrots are tender.
Mix in the tomato paste and cook for about another 5 minutes until it starts to turn light brown. Pour in the heavy cream and lemon juice and mix until combined. Add the chicken back into the pan along with any juices and the peas. Increase the heat to medium high until the sauce starts to simmer and the fat begins to separate from the sauce. Mix in the cilantro and season with 1½ teaspoons of kosher salt or to taste.
Roll out both rolls of the pie dough. Place one of the crusts into the bottom of a deep 9-inch pie pan. Add the butter chicken mixture into the pie pan and smooth into an even layer. Place the remaining pie crust on top. Slightly tuck the edges of the top crust under the bottom crust. Using both hands, hold your index finger and thumb as if you were about to pinch something then crimp together the edge of the crust, going all the way around.
Use a knife to create a few slits in the center of the top pie crust. In a small bowl whisk together the egg and water or milk until well combined. Brush a layer of the egg was onto the top crust until completely coated. Place the pie pan on top of a baking sheet in case it bubbles over.
Bake it in the oven for 30-40 minutes until golden brown. If the edges of the crust start to get too dark, cover them with strips of foil. Allow the pot pie to sit for 10 minutes before serving. Garnish with additional chopped cilantro if desired and enjoy!