Preheat oven to 400F. Place cubed sweet potatoes in a pot and cover with water. Pour 1 tbsp kosher salt into the pot and stir. Bring to a boil, reduce to a simmer, cover pot and let simmer for 10 minutes.

In a separate pan heat oil over medium heat and add the onions to the pan. Saute until fragrant 3-5 minutes. Add the ground turkey to the pan, brown and break into crumbles. Mix the seasonings into the ground turkey.

Add the chicken broth, tomato paste, and worcestershire sauce to the turkey mixture and stir to combine. Add the frozen mixed vegetables to the pan and mix in. Allow mixture to simmer for about 10 minutes.

When sweet potatoes are fork tender, drain the water and add yogurt, chicken broth and butter to the warm pot. Allow the butter to melt and then whip everything together with a hand mixer. Taste and add salt as needed.

Assemble in a casserole dish with an even layer of the meat mixture on the bottom. Top with the sweet potatoes and smooth into an even layer. Sprinkle on the parmesan cheese.

Bake uncovered for 20 minutes. If desired, increase oven heat to broil at the end to add some browning to the parmesan cheese.