1. Heat oven to 350 degrees.
2. In a medium saucepan heat olive oil. Add onion and saute until translucent. Add garlic and cook for about 1 more minute.
3. Place chicken in pan in a single layer. Cover with milk and add oregano and a pinch of salt and pepper.
4. Heat milk over medium heat until almost to simmering, but do not boil. Cover and cook until chicken is cooked through, about 10 minutes. Do not overcook as the chicken will continue to cook in the oven. When chicken is cooked through, remove and place on a cutting board to cool. Leave the milk in the saucepan but turn the heat to low.
5. Meanwhile, boil the chicken stock in a large pot and add potatoes and carrots. Cook until fork tender, about 10 minutes. Make sure to not overcook as they will continue to cook in the oven.
6. Once cooked, add the carrots and potatoes to the saucepan with the milk. Reserve the stock.
7. Once chicken has cooled chop into small pieces and add back to pan. Also add in peas at this point.
8. In a small bowl, mix the cornstarch with about ¾ cup of the reserved chicken stock using a whisk or fork. Make sure there are no lumps. Slowly add the mixture to the saucepan, gently folding in. If the mixture is too thick, add a bit more chicken stalk.
9. Pour mixture into a 2-quart casserole or pie dish. Top with your choice of puff pastry, phyllo dough or pie dough. I used phyllo dough because I love the light, flaky texture, but any dough will work. See notes for instructions.
10. Bake for about 25-30 minutes until the dough is cooked through and browned.
11. Let cool for a few minutes before serving. Enjoy!

Notes

You can top your pie with either puff pastry, phyllo dough or pie dough. I used phyllo dough because I love the light, flaky texture, but any dough will work. Follow the instructions on the package for the best result.