Preheat your oven to 375 °F and set aside an 8x8 baking dish.
Bring a large pot of water to a boil. Add in the peeled and chopped potatoes and 2 cloves of garlic and reduce the heat to a simmer. Allow the potatoes to cook until fork tender. Once cooked through, drain and rinse the potatoes and garlic and place them back in the same pot.
While the potatoes are cooking, start cooking the lentils. Place the 1 cup of lentils, 2 ½ cups of water and a bay leaf in a sauce pan and bring everything to a boil. Reduce the heat to a simmer and allow the lentils to cook until softened, but not overcooked, about 15 minutes.
Drain and rinse the lentils, remove the bay leaf, and set aside.
In a large skillet or sauce pan, heat 1 tablespoon of olive oil over medium heat.
Add in the chopped onion and saute until translucent, about 5 minutes.
Add in the carrots, celery and minced garlic and saute another 5 minutes or until the vegetables have softened.
Add in the frozen corn, tomato paste, tamari, herbs and salt and pepper to taste. Don't be shy with the salt! Allow everything to saute for a few minutes.
Add in the cooked and drained lentils and stir until everything is well combined.
While the vegetables are cooking you can continue preparing the mashed potatoes. To the boiled potatoes and garlic, add in the milk, nutritional yeast, olive oil, and a generous amount of salt and pepper.
Using a potato masher, mash everything together until the potatoes are smooth and everything is well combined. Taste and add more salt and pepper or nutritional yeast if desired.
Pour the lentil mixture into an 8x8 baking dish and use the back of a spoon to make the filling flat.
Spoon the mashed potatoes over the top of the lentils and evenly spread them out, making a fun, textured design with the back of your spoon if desired. You may not use all of the mashed potatoes.
Place the Shepherd's Pie into the preheated oven and allow it to bake about 30 minutes or until the mashed potatoes start to turn golden brown.
Removed from the oven and serve warm with freshly ground black pepper and parsley if desired.
Notes
*You can substitute the tamari sauce for soy sauce if not gluten-free.