If you haven't already, remove the puff pastry from the freezer and allow 1-2 hours to thaw.

Cut chicken breasts into small cubes. Heat a large, deep skillet over medium high heat and add oil. Add the chicken to the skillet, sprinkle with salt and pepper and cook for 4-5 minutes (stirring occasionally).

Add the chopped onion to the chicken and cook for 2-3 minutes, stirring frequently. Mix in the minced garlic and cook for 1 more minute. Add the butternut squash and cook for 4-5 minutes before finally adding the cauliflower and broccoli florets, mixing well. Cover the skillet, reduce heat to medium and allow vegetables to cook for 5 minutes

Remove the lid and add the cream cheese, butter, half and half, milk, salt + pepper, and dried parsley. Stir and cook over medium heat until the ingredients are combined and the cream cheese has fully dissolved.

Remove skillet from heat and stir in the shredded parmesan cheese and fresh chopped parsley. Pour into a greased 12-inch-cast-iron skillet. Cover skillet with a sheet of thawed puff pastry and brush with a beaten egg. Using a sharp knife, poke a few small holes through the top of the dough (they don't need to be big).

Place the skillet on a rimmed cookie sheet (to catch spills) and bake at 400 degrees for approximately 25 minutes, or until top is golden brown (you may need to rotate the skillet once half way though for even cooking). Remove from the oven and serve immediately.