Preheat oven to 350°F.
Dice all of the vegetables for the filling and set aside. Measure out the herbs and spices. Measure out the peas and place in a bowl.
Drain and rinse the navy beans and place in a bowl. Lightly mash about on third of the beans with the back of a fork or a potatoe masher and set aside.
Break up the cauliflower into florettes and place in steamer basket. Steam for about 10 minutes. If you do not have a steamer basket, gently simmer the cauliflower in enough water to cover for about 5 minutes, drain and set aside. The cauliflower should be fork tender.
Peel and dice potato and place in a steamer basket or in a large pot of water. Bring to a boil and steam or boil for about 15 to 20 minutes. Check doneness by piercing with a fork (should be very tender). Drain in a colander and set aside.
While the potatoes are cooking, start the filling by placing the avocado oil in a large pan or dutch oven and heat over medium heat.
Add onion, garlic, carrots, celery and mushrooms to the pan. Sauté for about 5 to 7 minutes, stirring occasionally.
Add tamari, Worchestershire sauce, tomato paste, turmeric, oregano, thyme, bay leaves, salt and pepper and vegetable broth.
Bring to a boil. Reduce heat, cover and simmer gently for 20 minutes, stirring occasionally.
Mix arrowroot starch with ½ cup of cold water. Add to pan. Bring back to a boil and boil 1 additional minute to thicken.
Turn down heat to medium low and add the peas and navy beans. Gently stir and heat mixture for about one minute. Turn off heat and set aside.
Place the cooked potatoes and cauliflower in a large bowl and add the olive oil, vegetable broth, salt and garlic powder. Mash together until fluffy.
Add the filling to a 9"x13" baking dish and top with potato-cauliflower mixture. Place on a baking tray if you feel that there is a chance the mixture may overflow. Alternatively, divide filling and topping amongst 8 ramekin dishes to make individual servings.
Place in oven and bake for 30 minutes. Sprinkle with fresh thyme or parsley if desired.
Let cool 15 to 20 minutes prior to serving.
Top off this meal by serving it with a side salad.