Cook ramen noodles according to package instructions (without the seasoning). Drain and set aside.
Heat olive oil in a large skillet over medium-high heat.
Season chicken with salt and pepper, then cook until golden and cooked through. Remove and set aside.
In the same skillet, sauté broccoli, bell pepper, and onion until slightly tender.
Add garlic and stir for 30 seconds until fragrant.
In a small bowl, whisk together soy sauce, brown sugar, sesame oil, ginger, red pepper flakes, and cornstarch slurry.
Return chicken to skillet, pour in sauce, and toss everything together.
Add cooked ramen noodles, mix until fully coated in sauce.
Cook for 2–3 more minutes until everything is heated through.
Garnish with sesame seeds and green onions before serving.