Strain the orange juice into a small pot. Add the orange zest, ginger, garlic, sugar, vinegar, soy sauce, and chili powder (if using), and bring to a low boil. Lower the heat slightly and simmer for 10 minutes, until the sauce has reduced by about a quarter. Whisk the cornstarch into the water, then whisk into the sauce. Cook over low heat, stirring constantly, until sauce has thickened, about 2-3 minutes. Set the sauce aside until ready to use.

Cut the cauliflower into even sized florets and place in a large bowl. In a medium bowl, combine the flour, cornstarch and salt and whisk together. In a small bowl, whisk together the eggs. Sprinkle half the the flour mixture over the cauliflower and toss well to coat. Pour the eggs over the dusted cauliflower and use a large spatula to mix well and make sure the cauliflower is completely washed with egg. Dump the second half of the flour mixture over the cauliflower and toss well again.

Fry the cauliflower in batches, making sure not to overcrowd the pot. As they come out of the oil, transfer to the baking rack to cool. Once all the cauliflower is cooked, combine it with the sauce and serve with rice, sesame seeds and sliced scallions.