Mix the sauce ingredients: In a small bowl or measuring cup, add soy sauce, orange juice, orange zest, brown sugar, rice vinegar, toasted sesame oil, and cornstarch. Whisk to combine.
Sauté aromatics: Add vegetable oil to a skillet. Add minced garlic, ginger, chili flakes, and the white parts of the green onions *before* turning on the heat. (This will help keep the garlic from burning.) Heat the pan over medium heat. Once it begins to sizzle, sauté for 2-3 minutes, or until the whites of the green onions are turning translucent and the mixture is very fragrant.
Make the sauce: Give the orange sauce mixture another whisk to redistribute the cornstarch, then pour the mixture into the pan with the scallions, garlic, ginger, and chili flakes. It should begin to simmer almost immediately. Stir constantly for 1-2 minutes, and the sauce should thicken up.
Final touches: Add the crispy tofu and the green parts of the scallions. Toss to coat, and serve immediately.