Begin with cooking your sweet potatoes. In a 5-6qt pot, add diced sweet potatoes and cover with at least 1 inch water. Bring pot to a boil, over medium-high heat until boiling.
When potatoes are boiling, reduce heat and let sweet potatoes simmer until very fork tender, about 18-20 minutes. Drain very well in a colander then return to warm pot off the heat.
Stir in remaining sweet potato mash ingredients and mash with a potato masher until smooth and all combined. Set aside covered to keep warm.
Meanwhile, make your turkey chili filling, once you get your sweet potatoes on to cook. Arrange a 10-12 inch medium-large cast iron or high-lipped saute pan over medium-high heat.
Add your olive oil and vegetables, sautéing 2-3 minutes until vegetables begin to soften. Push the vegetables to the outer circle of the pan and add ground turkey in the middle.
Break turkey up a bit with a spatula then leave undisturbed, 2-3 minutes to brown. Continue to break up turkey and add spices: chile powder, cumin, salt and pepper. Continue to stir and saute until vegetables are very tender and all turkey is cooked through, approximately 5-6 minutes.
Stir in bone broth and crushed tomatoes. Bring to a boil then reduce heat and let turkey chili simmer 20-25 minutes while sweet potatoes are cooking and you make your mashed topping.
When turkey chili is finished simmering and most of the liquid has been absorbed, turn off heat and evenly transfer your sweet potato mash atop. Smooth the top with a spatula then transfer to the top oven rack with the broiler on HIGH for 6-8 minutes until bubbling.
Let shepherd's pie cool 5-10 minutes before serving. Serve with more fresh cilantro and sliced avocado.