Preheat Oven to 350 Degrees F.
If chicken is not cooked, place breasts on a pan and boil it with water or chicken stock until thoroughly cooked. Remove from heat and dice in small pieces
Place 1 pie crust in a round pie plate. Prick holes with a fork all over the surface to prevent it from bubbling up. Bake for 10 minutes and remove from oven and let cool
Meanwhile, heat the olive oil on a big skillet over medium heat
Add the onions and cook until softened. Season with salt and pepper
Add the mushrooms and cook until reduced. Toss in the thyme and the tomato. Stir until combined
Finally, toss in the chicken and mix
Add the chicken mixture into the pre-baked pie dough
Add the ricotta cheese on top covering the whole surface
Cover with the remaining pie dough and cut a few slits on top
Brush the entire pie top with the egg
Add salt and pepper
Bake for 20 minutes or until the pie is golden
Remove from oven and cool for 5-10 minutes before slicing
Enjoy!