Preheat oven to 400°F (200°C).
Peel the sweet potato and cut into 1-inch chunks, then place in a pot of water, bring to a boil, and cook for 12-15 minutes until soft.
While potatoes cook, heat olive oil in a large skillet over medium heat and sauté diced onion and carrots for 5 minutes until softened.
Add the ground turkey to the skillet, breaking it up with a spoon, and cook until browned.
Stir in the cooked lentils, tomato paste, dried thyme, garlic powder, sea salt, and black pepper.
Pour in the vegetable broth and add the frozen peas, then simmer for 5-7 minutes until the liquid has reduced into a thick gravy.
Drain the sweet potatoes and mash them thoroughly with the nutritional yeast until smooth and creamy.
Transfer the turkey and lentil mixture to a small baking dish and spread the mashed sweet potato evenly over the top.
Bake for 15 minutes, then broil for 2-3 minutes until the sweet potato topping is lightly golden and crisp.