Preheat the oven to 400 degrees F (200 degrees C). Line a baking sheet with parchment paper.
Peel sweet potatoes and cut into 1-inch rounds. Place on the prepared baking sheet and brush with 1 to 2 teaspoons oil.
Bake in the preheated oven until tender, 10 to 15 minutes.
Meanwhile, heat 2 tablespoons olive oil in a large Dutch oven over medium heat. Stir in onion, then add the beef substitute, breaking it into crumbles as it cooks. Use a wooden spoon to break the beef substitute up further while sauteing and cook until onion is translucent, about 5 minutes.
Add frozen peas and carrots, cooked lentils, vegetable broth, tomato paste, and yeast extract; mix until well combined and bring to a simmer. Simmer until thickened, about 5 more minutes, or until sweet potato topping is ready. Season with salt and pepper; it will be soupy.
Remove sweet potatoes from the oven and transfer to a mixing bowl. Reduce oven temperature to 375 degrees F (190 degrees C).
Mash sweet potatoes, and drizzle in remaining olive oil and almond milk. Whisk energetically with a fork, or use a stand mixer or hand mixer to fluff up the potatoes.
Remove the Dutch oven from the stovetop and spread sweet potato mixture evenly over top.
Bake uncovered in the preheated oven until bubbly and sweet potato topping has browned, about 35 minutes. Allow to cool slightly before serving.