Preheat your oven to 400°F (200°C).
Peel and chop the Yukon gold potato into small chunks, then boil in a pot of salted water until tender, about 12-15 minutes.
While the potato cooks, finely dice the carrots and onion.
In a large skillet, sauté the carrots and onion with a splash of water or vegetable broth over medium heat until they begin to soften.
Stir in the cooked lentils, frozen peas, tomato paste, tamari, dried thyme, and the remaining vegetable broth.
Simmer the lentil mixture for 5 minutes, allowing the liquid to reduce and form a thick, savory gravy.
Drain the cooked potatoes and return them to the pot.
Add the Greek yogurt, nutritional yeast, and garlic powder to the potatoes, mashing until the mixture is smooth and creamy.
Transfer the lentil and vegetable filling into an oven-safe baking dish, spreading it into an even layer.
Top the filling with the potato mash, using a fork to create textured ridges across the surface.
Bake for 15-20 minutes until the filling is bubbling and the potato topping is lightly browned and crisp on the edges.
Season with sea salt and black pepper before serving hot.