Preheat oven to 350°F (176°C). While the potatoes are cooking, start preparing the filling. In a large deep 12-15 inch cast-iron skillet, over medium-high heat, drizzle oil and add in 1 tablespoon of vegan butter.
Add chopped or sliced onions, chopped celery, and chopped carrots and cook down until softened for 3 minutes. Then add your mushrooms, and cook for an additional 3 to 4 minutes until mushrooms are tender. If needed add more oil so that the vegetables don't stick to the pan.
Next add in garlic paste (crushed garlic), tomato paste, rosemary, sea salt, pepper, and chickpea flour and mix thoroughly completely coating your vegetables with the flour.
To your vegetables, add in water, vegetable bouillon, and red wine. Mix to fully combine. Then add in lentils and peas and mix together into your sauce. Reduce heat to low and simmer uncovered for about 12 minutes until your sauce thickens slightly.
Once the filling is done, remove from heat. In your cast-iron skillet, carefully top with mashed potatoes. Evenly smooth down with a spoon or rubber spatula. Use a fork to lightly comb over your potatoes creating texture and design to your potato crust.
NOTE: If you DO NOT have a cast-iron skillet, cook your filling in a large pot or large deep skillet. When done, transfer filling into a lightly grease a 2-quart baking dish or 9x13 baking pan. Then proceed to top with mashed potatoes.
Drizzle with additional oil or vegan butter to create that browning effect and sprinkle fresh parsley on top (optional).
Add a baking sheet or pizza pan to your oven and place your cast iron skillet or baking dish on top. This is to catch the overflow of the filling. Bake in your preheated oven for about 25 minutes until top is golden brown.
Let cool briefly before serving as the longer it sits, the more it will thicken and be easier it will be to see those two layers between potatoes and filling. Serve with a large green saladb or additional steam vegetables.
Divide evenly into 6 portions storing in individual containers for meal prepping. (Or you can keep it in your baking dish covered). Leftovers keep covered in the refrigerator 5-6 days and can be frozen for up to 1 month covered. If frozen, thaw in the refrigerator overnight and reheat in the microwave or oven.