Prep everything first. Cut the chicken into small pieces so it cooks quickly.
Dice the onion, mince the garlic, and slice the mushrooms, broccoli, and carrots. Open the ramen and discard the seasoning packets.
Sear the chicken. Heat the oil in a large skillet over medium-high heat. Add the chicken in an even layer, season with a pinch of salt and black pepper, and cook until lightly browned and just cooked through, 4–6 minutes.
Transfer to a plate.
Sweat the aromatics. In the same skillet, reduce heat to medium. Add onion and cook until soft and translucent, about 3 minutes. Stir in the garlic and cook 30 seconds until fragrant.
Cook the veggies. Add mushrooms, broccoli, and carrot.
Cook, stirring occasionally, until the mushrooms release moisture and the broccoli is crisp-tender, 3–4 minutes. If the pan looks dry, splash in a tablespoon of broth.
Build the sauce base. Pour in the chicken broth, soy sauce, oyster sauce, and red pepper flakes. Scrape up any browned bits.
Bring to a gentle simmer.
Add the ramen. Break the ramen bricks in half and nestle them into the simmering liquid. Cover and cook 2 minutes, then flip the noodles and use tongs to separate as they soften.
Stir in the cream. Reduce heat to medium-low. Pour in the heavy cream and simmer gently, tossing the noodles so they absorb the sauce.
If it thickens too fast, add a splash of water or more broth.
Finish with chicken and cheese. Return the chicken (and any juices) to the pan. Sprinkle in the Parmesan and stir until melted and the sauce turns glossy and creamy. Drizzle in the toasted sesame oil.
Taste and adjust salt and pepper.
Garnish and serve. Top with scallions and sesame seeds. Squeeze a little lime over each bowl if you like a bright finish. Serve hot.