Heat your cast iron pan to medium-heat. Add olive oil (or your favorite oil) and ground chicken. Brown the chicken until it is mostly cooked through.
To the same pan, add all the veggies under "Filling". Be sure all veggies are chopped to the same size so they cook at the same time.
In the meantime, boil a pot of water. Peel and roughly chop your sweet potatoes. Add potatoes to the boiling water and salt liberally.
When veggies are fork tender, add the tomato paste, chicken broth and rest of the seasonings under "Filling". Simmer until the chicken broth is mostly absorbed and sauce is thick. If it does not thicken, add a small amount more of the tomato paste.
When your sweet potatoes are tender, drain and put in a mixing bowl with the rest of the "Mashed Potato" ingredients. Mix until smooth. *Note: I do this in my Kitchen Aid mixer, but a hand mixer or potato masher will work*
When mashed potatoes are smooth, spread on top of the filling. Put the pan in the oven on 400° F degrees, uncovered for 20 minutes.
If the top is not browned, turn your oven on broil for another 5 minutes or until the potatoes are lightly browned on top.