Preheat your oven to 400°F (200°C).
Place the dried lentils in a small pot with 1 cup of water. Bring to a boil, then reduce heat and simmer for 15-20 minutes until tender. Drain any excess water.
While lentils cook, peel and chop the parsnip and cauliflower. Steam or boil them for 12-15 minutes until very soft.
Drain the parsnips and cauliflower, then mash them thoroughly with the Greek yogurt, sea salt, and black pepper until smooth and creamy.
In a large skillet, heat the olive oil over medium heat. Sauté the diced onion, carrots, and minced garlic for 5 minutes until softened.
Crumble the tempeh into the skillet. Add the cooked lentils, tomato paste, tamari, thyme, and rosemary. Stir to combine.
Pour in the vegetable broth and simmer for 5 minutes until the liquid has thickened into a light gravy.
Transfer the lentil and tempeh mixture to a small baking dish. Spread the root vegetable mash evenly over the top.
Bake for 15-20 minutes until the topping is lightly browned and the edges are bubbling.
Let sit for 5 minutes before serving to allow the filling to set.