In a small bowl, mix together the Italian seasoning, oregano, garlic powder, fennel seeds, salt, black pepper, and red pepper flakes. Set aside.
Place a large skillet over medium-high heat. When the skillet is hot, add the oil and swirl the pan to coat. Add the ground turkey to the skillet and use a spoon or spatula to break it up. Sprinkle with the seasoning mix and cook for 3 minutes, stirring once, then add the onions and garlic and continue to cook for another 5-7 minutes or until the turkey is no longer pink and the onions just start to soften, stirring occasionally.
Transfer the turkey mixture to the slow cooker. Add the potatoes, mushrooms, and chicken broth; stir gently to combine.
Place the lid on the slow cooker and cook for 6 hours on LOW (or 3 hours on HIGH) or until the potatoes are just tender. Increase the temperature setting to high.
In a small bowl or glass measuring cup, whisk the cornstarch into the half and half. Add the half-and-half to the slow cooker and stir. Replace the lid and allow the soup to cook for 30 minutes.
Remove the lid and stir in the kale. Replace the lid and cook for another 20-30 minutes stirring occasionally.
Ladle the soup into bowls and garnish with Parmesan cheese, parsley, and additional red pepper flakes.
