Set the oven to 425°F. Line two sheet pans with parchment. Lightly oil or spray.
Pat chicken dry. Toss with salt, pepper, and garlic powder.
Add cornstarch and panko to a bowl. In another bowl, whisk eggs. Dip chicken in egg, then coat in the cornstarch-panko mixture. Press lightly so it sticks.
Place coated chicken on one sheet pan. Spray generously with oil for max crisp.
Toss florets with olive oil and salt. Spread on the second sheet pan.
Put both pans in the oven. Bake 15 minutes. Flip chicken and stir broccoli. Bake another 8–10 minutes until chicken is golden and 165°F internal, broccoli is tender-crisp.
While baking, whisk orange juice, zest, soy sauce, rice vinegar, honey, brown sugar, sesame oil, garlic, ginger, and red pepper flakes in a skillet. Bring to a simmer over medium heat for 3–4 minutes.
Stir in cornstarch slurry. Simmer 1–2 minutes until glossy and thick enough to coat a spoon. If too thick, splash in water. If too thin, simmer another minute.
Add baked chicken to a big bowl. Drizzle in only enough sauce to coat —about 2/3 of it—then toss quickly. Add broccoli and toss again. Reserve extra sauce for serving so the chicken stays crisp.
Spoon over rice, top with sesame seeds and scallions. Add more sauce if you're a sauce boss.