Prepare the Sauce: In a small bowl, whisk together the water, soy sauce, brown sugar, rice wine vinegar, toasted sesame oil, ginger paste, minced garlic, cornstarch, white pepper, and Chinese five spice (if using). Set aside.
1/3 cup water, 1/3 cup soy sauce, 1/4 cup brown sugar, 2 Tablespoons rice wine vinegar, 1 Tablespoon toasted sesame oil, 1 Tablespoon ginger paste, 8 cloves garlic, minced, 1 Tablespoon cornstarch, 1/4 teaspoon white pepper, 1/4 teaspoon Chinese five spice, optional
Marinate the Beef: In a medium bowl, toss the sirloin with 2-3 tablespoons of the sauce. Let this marinate while you prepare the broccoli and noodles.
1 pound sirloin steak, thinly sliced
Cook the Broccoli: Bring a large pot of salted water to a boil and blanch the broccoli florets for 2-3 minutes, until bright green and tender-crisp. Drain and set aside, adding some ice on top to stop the cooking.
6 cups broccoli florets
Cook the Noodles: In the same pot, cook the lo mein noodles according to the package instructions until al dente. Drain and rinse well with cold water, then set aside.
8 ounces dried lo mein noodles
Sauté the Onion: In a large wok or large skillet over medium heat, add the avocado oil. Add the onion and sauté for 2-3 minutes, until softened and slightly translucent.
1 1/2 Tablespoons avocado oil, 1/2 white or yellow onion, diced finely
Sear the Beef: Increase the heat to medium-high. Add the thinly sliced sirloin steak and sear for a few minutes until caramelized and cooked through.
Combine: Reduce the heat to medium. Add the cooked noodles and the remaining sauce to the wok, tossing gently until the sauce thickens. Lastly, toss in the broccoli.