Bring a large pot of water to a boil. Add the noodles and cook according to the package directions, cutting off 1 to 2 minutes from the cook time, so the noodles are al dente.
While the noodles cook, stir together the orange juice, soy sauce, maple syrup, sriracha, garlic, and ginger in a small saucepan. Place over medium heat and bring it to a simmer. Allow to simmer for about 10 minutes. Stir the water and cornstarch together in a small bowl or cup, then add it to the sauce and stir a few times. Allow to simmer 1 minute more, then remove from heat.
Coat the bottom of a large skillet with oil and place over high heat. When the oil is hot, add the broccoli and white parts of scallions. Stir-fry for about 2 minutes, until the broccoli's color intensifies a bit. Add the noodles and sauce. Continue to stir-fry until the liquid cooks off and the noodles begin to crisp, about 2 to 4 minutes, depending on how crisp you'd like the noodles to be. Remove from heat and add in the sesame seeds and green parts of scallions.
Divide onto plates and sprinkle with extra sesame seeds and red pepper flakes, if desired.