Preheat the oven to 425ºF.
Cook the quinoa (if using) in water or vegetable broth according to the directions on the packet. Fluff with a fork and set aside to cool.
In a wide bowl or small rimmed baking sheet, mix the flour, baking powder, Italian seasoning, and salt. Add the milk to a separate wide bowl.
Transfer the quinoa to separate wide bowl or rimmed baking sheet.
Using a pair of tongs, dip all sides of the tofu rectangle into the nondairy milk, then into the flour mixture until evenly coated. Then dip it into the quinoa and use the back of a spoon to press the quinoa onto the front and back of the tofu rectangle until evenly coated. Place the coated tofu onto a large nonstick baking sheet or parchment-lined sheet. Repeat for the other seven tofu rectangles.
Bake the tofu for 15 minutes. Gently flip the rectangles over and bake for about 10 minutes more, or until crispy and golden-brown.
Meanwhile, mix the lime juice, mayonnaise, rice vinegar, and sriracha in a small bowl.
Serve the crispy baked tofu with rice, cucumber slices, green onion, sesame seeds, and a generous drizzle of the spicy mayo sauce.