Prepare the lentils by cooking them in vegetable broth until tender, about 20-25 minutes.
In a large skillet, heat oil and sauté the onion and garlic until translucent.
Add the diced carrots and cook until slightly softened, about 5 minutes.
Stir in the peas, corn, tomato paste, soy sauce, thyme, and pepper, mixing well.
Add the cooked lentils to the vegetable mixture and stir to combine. Simmer for 5 minutes.
Preheat your oven to 400°F (200°C).
Boil the potatoes in salted water until tender, about 15 minutes.
Drain the potatoes and mash them with milk and butter until smooth.
Layer the lentil and vegetable filling in a baking dish and top with mashed potatoes.
Bake in the preheated oven for 25-30 minutes or until the top is golden and the filling is bubbling.