In a medium pot, combine the rice, water, salt, rice vinegar, sugar and sesame oil. Bring to a boil over high heat, then reduce the heat to low, cover, and simmer for 25 minutes, or until the water is absorbed and the rice is tender. Remove from heat and let sit, covered, for ten minutes.
Heat oil in a sauté pan for 90 seconds over medium heat. Once the oil is hot, crumble the dried tofu into the pan and sauté it for 7-8 minutes, stirring regularly until the tofu is golden and crispy in some spots.
Add the tamari, vegan oyster sauce, sriracha and scallions and continue to sauté for 2 minutes until the scallions have wilted, and the tofu has absorbed the seasonings. Remove the pan from the heat and set the tofu topping aside.
In a covered pan, combine the diced sweet potatoes (you can peel them, but I usually don't bother with that), water, sesame oil, tamari, maple syrup, rice vinegar, and shichimi togarashi (if using). Cook over medium heat, covered, until the sweet potatoes are tender and the liquid is absorbed, stirring occasionally. Remove from heat and set aside.
In a small bowl, whisk together vegan mayonnaise, sriracha, rice vinegar, and water until smooth using the tines of a fork or a tiny whisk. Set aside.
In another small bowl, whisk together vegan mayonnaise, wasabi powder, spirulina powder (if using), sesame oil, tamari, rice vinegar, and water until smooth. Set aside.
Preheat the oven to 375°F (190°C). Spread the sushi rice evenly in the bottom of a baking dish. Layer the tofu mixture on top of the rice, followed by the cooked sweet potatoes. Drizzle with sriracha mayo. Bake in the preheated oven for 15-20 minutes until heated throughout.
Remove from oven and garnish with diced cucumber, sliced scallions, diced avocado, and roasted sesame seeds. Drizzle with the wasabi mayo and then garnish with furikake. Serve with roasted seasoned laver (nori) on the side.