Boil the lo mein noodles according to package instructions until al dente. Drain and set aside.

In a small bowl, whisk together the soy sauce, brown sugar, sesame oil, and black pepper to make the sauce base.

Heat the vegetable oil in a large wok or skillet over high heat. Add the sliced steak and sear for 2-3 minutes until browned. Remove the steak from the pan and set aside.

Reduce the heat to medium. Add the butter and minced garlic to the same pan, stirring constantly for about 1 minute until fragrant but not burned.

Add the broccoli florets and a splash of water (about 1 tbsp) to the pan. Cover and steam for 2 minutes until the broccoli is bright green and tender-crisp.

Return the cooked steak and the noodles to the pan.

Pour the sauce mixture over the noodles and toss everything together using tongs. Stir-fry for another 2-3 minutes until the sauce coats the noodles and everything is heated through.

Remove from heat, garnish with chopped green onions, and serve immediately.