In a large pot, combine vegetable broth, water, onion, garlic, ginger, cinnamon sticks, star anise, whole cloves, soy sauce, hoisin sauce, and brown sugar. Bring to a boil, then reduce heat and let it simmer for around 30 minutes to allow the flavors to infuse.
Using a fine-mesh strainer or cheesecloth, strain the broth to remove the solid ingredients. Return the broth to the pot and keep it warm over low heat.
In a skillet, heat some oil over medium heat. Add tofu slices and cook until golden brown, about 3-4 minutes per side.
In the same skillet, add mushrooms and sauté for about 5 minutes, until cooked and tender. Set aside.
To assemble the Vegan Pho Tai, place cooked rice noodles in the bottom of a bowl. Top with cooked tofu, mushrooms, and mixed vegetables.
Pour the hot broth over the noodles and vegetables. Garnish with fresh herbs, a squeeze of lime, and sriracha or chili sauce if desired.