Preheat the oven to 400°F.
In a medium saucepan, steam the cauliflower and diced sweet potato until very tender, about 10 minutes.
Meanwhile, heat a non-stick skillet over medium heat and add the olive oil. Sauté the chopped onion, minced garlic, and diced carrot until softened, about 3-4 minutes.
Add the lean ground turkey to the skillet, breaking it up with a spoon. Cook until the turkey is browned and nearly cooked through, about 5-6 minutes.
Stir in the low-sodium chicken broth and let the mixture simmer for 3 minutes to meld the flavors. Season with salt, pepper, and a pinch of thyme or your preferred dried herb.
Transfer the turkey and vegetable mixture into a small oven-safe baking dish.
Drain the steamed cauliflower and sweet potato. Blend them together until smooth, adding a splash of the chicken broth if needed to achieve a creamy texture. Season lightly to taste.
Spread the creamy cauliflower-sweet potato mixture evenly over the turkey layer.
Bake in the preheated oven for 15-20 minutes, until the topping has set and the edges are slightly golden.
Allow the dish to cool for a few minutes before serving. Enjoy your balanced, comforting shepherd's pie!