Bring a medium saucepan over medium heat. Add 1 tsp of oil to the pan. Once melted, add the chopped onion and garlic. Saute until brown. Then add the celery, carrots and thyme. Saute for a few minutes.
Rinse the lentils and set aside. Add the red wine to the veggie mixture and let it incorporated into the veggies for a few minutes. Next, add the rinsed lentils and mix the lentils into the veggies.
Add 2 tbsp of flour to coat the veggie/lentil mixture.
Add 3 cups of veggie broth and bring the filling mixture to a boil. Cover with a lid and reduce to a simmer. Add the salt and pepper. Simmer for 10-15 minutes until the lentils and carrots are soft. Stirring the mixture every few minutes so it doesn't stick on the bottom of the pan. Add the frozen peas to the filling mixture with 5 minutes left to simmer.
Preheat your oven to 350ºF.
Once the filling mixture is cooked, add the mixture to a 10x10 pan (3 inches deep). Top the filling with the mashed potatoes, and smooth the potatoes out evenly over the filling.
Bake for 25 minutes. Then turn the broil on to brown up the top of the shepherd's pie. Mine broiled for about 2 minutes. But watch this closely. Option to top shepherd's pie with ketchup and chives.
Store leftovers in an airtight container in the fridge for 4 days.