Preheat oven to 425 degrees. Line large sheet pan with parchment paper.
Cut cauliflower into bite size pieces
Separate flour into two bowls, 1 cup of flour in each bowl. Add 1 cup of warm water to one of the bowls of flour. Mix to create a batter, add more water if needed.
Season dry flour with salt, pepper, garlic powder, and cayenne
Dip each cauliflower in wet flour mixture and then coat with dry mixture. Space cauliflower pieces on parchment paper lined sheet pan.
Bake 10 minutes, flip and bake an additional 10 minutes. Remove cauliflower from oven. Make sauce while cauliflower is baking.
In a small saucepan combine orange juice, soy sauce, mirin, red pepper flakes, and garlic powder. In a separate bowl mix together 1 tbsp of cornstarch with 2 tbsp water. Mix cornstarch mixture into saucepan over medium heat. Once bubbling, reduce to low until thickened about 3 minutes.
Toss cauliflower with sauce and return to sheet pan. Return to oven for additional 5 minutes.
Serve over rice and garnish with green onions
