Preheat the oven to 450°F. Line a baking sheet with parchment paper or lightly rub it with some of the extra virgin olive oil.
In a bowl, combine the cubed chicken, 2 tablespoons orange zest, and black pepper. Add 1/4 cup flour (or gluten-free flour) and toss until the chicken pieces are evenly coated. Drizzle 2 tablespoons extra virgin olive oil over the coated chicken and toss to coat.
Arrange the coated chicken in a single layer on one side of the prepared baking sheet.
Place the 3 cups broccoli florets on the other side of the baking sheet. Drizzle the remaining 2 tablespoons extra virgin olive oil over the broccoli and toss with black pepper to coat. Spread the broccoli in a single layer.
Bake the chicken and broccoli in the preheated oven for 15–20 minutes, until the chicken is cooked through and the broccoli is tender-crisp.
While the chicken and broccoli bake, make the sauce: in a saucepan combine 1 cup fresh orange juice, 2 tablespoons orange zest, 1/3 cup tamari or soy sauce, 2 tablespoons rice vinegar, 3 tablespoons honey, 4 grated garlic cloves, 1 tablespoon grated fresh ginger, 3–4 tablespoons chili paste (gochujang), 1 tablespoon toasted sesame oil, and 1 tablespoon cornstarch (or flour). Whisk the mixture until the cornstarch or flour is fully dissolved and the sauce is smooth.
Set the saucepan over medium heat and bring the sauce to a simmer, stirring, until it bubbles and begins to thicken, about 3–4 minutes. Remove the sauce from the heat.
Remove the sheet pan from the oven. Transfer the broccoli to a plate and set aside. Pour the hot orange-chili sauce over the chicken on the sheet pan and toss the chicken in the sauce so pieces are evenly coated.
Return the sauced chicken (on the sheet pan) to the oven and bake about 5 minutes more, until the sauce has thickened and glazed the chicken.
Remove from the oven and serve the chicken and broccoli topped with sliced green onions and sesame seeds.