Start a pot of water boiling for your noodles (unless you're microwaving them). You'll be cooking them according to the directions on the packet.
In a medium-sized bowl, combine the chicken stock, dark soy sauce, oyster sauce, mirin, and cornstarch. Set aside.
Season the chicken lightly with salt. Heat a large wok or skillet over medium-high heat and add 1 tablespoon of the oil. When hot, add the chicken and cook, stirring often, until cooked through, about 5 minutes. Transfer the cooked chicken to a clean bowl and set aside.
Add the remaining tablespoon of oil to the wok. When hot, add the broccoli and cook, stirring, for about 3-4 minutes. The broccoli should be starting to char around the edges, but it will cook more in the sauce so it doesn't need to be completely tender.
Add the garlic and cook, stirring, for 30 seconds or so. Give the sauce a stir and add it to the wok along with the cooked chicken. Bring to a simmer, stirring often.
This is a good time to cook your noodles! Add them to the boiling pot of water and drain in a colander when done.
When the sauce thickens and the broccoli is done to your liking, stir in the cooked noodles.
Serve noodles in plates or bowls, topped with sliced green onion if you like.