In a large pan over medium heat, saute the diced onion in 3-4 tbsp vegetable broth until soft. Add minced garlic, 1 tbsp Italian seasonings, ¼ tsp black pepper, ¼ cup tomato paste, 1 tbsp vegan Worcestershire, and 1 tbsp tamari to the pan, stir, and let it cook until fragrant.
While the onions are cooking, put the purple potatoes into a large pot with cool water. Bring it to a boil and let the potatoes cook for 20 minutes or until they're fork tender. Drain the water. Add ½ cup unsweetened almond milk, 2 tbsp vegan butter, 1 tsp garlic powder, salt and pepper (to taste) and then mash until creamy.
Add the quartered mushrooms, frozen vegetables, and ½ cup red wine to the pan with the onions and let it cook until the vegetables are tender and the wine has reduced. Stir in the cooked chickpeas.
Pour 1 cup lukewarm vegetable broth in a separate bowl and whisk in 2 tsp arrowroot powder until it has dissolved. Pour the mixture into the pan with the vegetables and stir to combine. Let it cook for a few minutes until the sauce starts to thicken.
Preheat the oven to 350 degrees.
Pour the vegetable mixture into a large casserole dish and spread it out. Spread the mashed potatoes evenly over the vegetable filling.
Sprinkle vegan shredded cheese over the mashed potatoes and bake for 30 minutes. To get more color on the mashed potatoes, broil the casserole for an additional 4-5 minutes.
Remove the casserole from the oven and let it sit for 5 minutes to set up before serving. Garnish with parsley.