In a pan over medium-high heat, heat the vegan butter or olive oil.
Add the mushrooms, carrots, garlic, onion, celery and thyme. Stir together and allow to cook until onion is translucent and the garlic is fragrant, and veggies are cooked down, about 10 to 12 minutes. Stir, and add salt and pepper to taste.
Add the flour, and stir to coat, then pour in the vegetable broth. Allow to simmer for 5 more minutes on medium heat for the mixture to thicken slightly. If you want a thicker filling, add in more flour by the tablespoon. Remove from heat and add in the cooked lentils and peas and stir, allowing the mixture to heat through the frozen peas. Add more salt and pepper if needed here after tasting.
Pour into a casserole dish and spread the mashed potatoes over the top, covering completely. You can shape it into a little design if you'd like.
Bake for 15 minutes, then broil on low until the mashed potatoes top is golden brown.
Allow to cool slightly, then serve. Enjoy!
*This recipe is vegan and gluten-free.
To store in fridge: You can store this in its original container with a lid, or transfer to an airtight tupperware container in the fridge for up to 5 days.
To reheat: Simply microwave, or reheat in oven at 350 degrees until warm (about 10 minutes) to keep top crispy.
Freezing: You can freeze the entire casserole for later, or freeze your leftovers. Wrap the Shepherd’s Pie tightly or transfer it to an airtight container, then freeze for up to 2 months.