This dish delivers horde-sized flavors without you having to roam around for a take-out menu. Leafy Chinese broccoli, or gai lan, brings a beautiful, slightly bitter, flavor to the dish. Add that to the green onions and sirloin steak strips being finished in a balanced sauce of salt, sweet, and heat. Place this meaty stir-fry on top of a bed of rice, and you have a meal fit for a king, or khan.
Trim ¼" off ends of Chinese broccoli and halve stalks, separating stems from leafy tops. Cut stems into 2" pieces. Coarsely chop tops. Mince garlic. Trim and cut green onions into ½" pieces. Coarsely chop peanuts. Season steak strips with a pinch of salt and pepper.
Cook the Rice
Bring a small pot with rice and 1 cup water to a boil. Reduce to a simmer, cover, and cook until tender, 18-20 minutes. Remove from burner and fluff rice. Cover again and set aside. While rice cooks, roast broccoli.
Roast the Broccoli
Place Chinese broccoli, stems and tops, on prepared baking sheet. Toss with 2 tsp. olive oil, ¼ tsp. salt, and a pinch of pepper. Spread into a single layer and roast until tender, 6-8 minutes. While broccoli roasts, start steak.
Sear the Steak Strips
Heat 2 tsp. olive oil in a medium non-stick pan over medium-high heat. Place sirloin steak strips in hot pan. Cook undisturbed until browned, 1-2 minutes. Transfer to a plate. Steak strips will finish cooking in a later step. Reserve pan; no need to wipe clean.
Make Sauce and Finish Steak
Add garlic and 1 tsp. olive oil to pan used to sear steak strips over medium-high heat. Stir constantly until fragrant, 30 seconds. Add soy sauce, brown sugar, and a pinch of red pepper flakes (to taste) (reserve remaining for garnish). Bring to a simmer, and cook, stirring occasionally, until sauce thickens, 3-4 minutes. Stir in steak strips and green onions, and cook until no pink remains on steak, 1-2 minutes.
Plate the Dish
Toss Chinese broccoli with steak strips, green onions, and sauce. Place a serving of rice on a plate. Add Mongolian beef and garnish with chopped peanuts and remaining red pepper flakes (to taste).