Preheat the oven to 375°F (190°C).
For the meatless filling:
In a large skillet, heat olive oil over medium heat. Add diced onions and garlic, and sauté until softened. Add all remaining meatless filling except for the walnuts. Bring the mixture to a simmer, lower the heat, and cover it to cook for about 15 minutes until all the broth is absorbed. It's ready when lentils are soft. If it runs too dry, add a little water. Add in the walnuts and remove from heat. For the Mashed Potato Topping:
Boil the diced potatoes in a large pot of salted water until fork-tender. Drain the potatoes.
In a bowl, mash the potatoes with soy milk, vegan butter, salt, and pepper until smooth and creamy.
Assemble the pate chinois:
Transfer the meatless filling to a large baking dish, spreading it evenly.
Then, add the layer of the drained canned corn before spooning on the mashed potatoes to cover the pie completely. Sprinkle top with paprika.
Place the baking dish in the oven and bake for 25-30 minutes or until the top is golden brown. For an extra crispy potato topping, broil the top to finish. Watch closely to avoid burning.