In a large saucepan of 2 cups water, cook rice according to package instructions; set aside.
Heat vegetable oil in a large stockpot or Dutch oven over medium high heat until temperature reaches 375 degrees F.
In a medium bowl, whisk together cornstarch, baking powder, salt, egg and beer.
Working in batches, dip cauliflower into cornstarch mixture, allowing excess to drip off.
Add cauliflower to the Dutch oven, 5 or 6 at a time, and cook until evenly golden and crispy, about 3-4 minutes. Transfer to a paper towel-lined plate.
In a large saucepan over medium low heat, combine chicken stock, orange juice, sugar, vinegar, soy sauce, garlic, orange zest, Sriracha, ginger and cornstarch. Bring to a boil; reduce heat and simmer, stirring constantly, until slightly thickened, about 2-3 minutes. Stir in cauliflower.
Serve immediately with rice, garnished with green onions and sesame seeds, if desired.