Cook the pasta. Bring a large pot of salted water to a boil. Cook pasta until just shy of al dente. Reserve 1/2 cup pasta water, then drain. Toss with a drizzle of oil to prevent sticking.

Prep the sauce. Zest both oranges, then juice them (aim for 3/4 cup). In a bowl, whisk orange juice, half the zest, soy sauce, rice vinegar, brown sugar or honey, chicken broth, and cornstarch until smooth.

Season the chicken. Pat chicken dry. Season with salt and pepper. If you like a light crust, dust with 1 teaspoon cornstarch.

Sear the chicken. Heat 1 tablespoon oil in a large skillet over medium-high. Cook chicken in a single layer, undisturbed, until browned on one side, 3–4 minutes. Flip and cook through, 2–3 minutes more. Transfer to a plate.

Sauté aromatics. Add remaining oil to the pan. Stir in garlic, ginger, and a pinch of red pepper flakes. Cook 30 seconds until fragrant, scraping up browned bits.

Build the sauce. Whisk the orange sauce again (cornstarch settles). Pour into the pan. Simmer over medium heat, stirring, until thick and glossy, 2–3 minutes.

Combine. Return chicken and any juices to the pan. Add cooked pasta. Toss until coated. If it seems tight, loosen with splashes of reserved pasta water until silky.

Finish. Stir in sesame oil, remaining orange zest, half the scallions, and half the sesame seeds. Taste and adjust salt, vinegar, or sweetness.

Serve. Top with remaining scallions and sesame seeds. Add more chili for heat if you like.

Optional veggies. If using snap peas, peppers, or broccoli, sauté them right after the aromatics, before adding the sauce. Cook until crisp-tender.