Place sliced beef into a sealable bag with cornstarch and toss to coat evenly. Allow to sit at *room temperature until you are ready to cook it in later steps. Peel and mince ginger and garlic. Thinly slice green onions, separating the whites from the greens. Dice red peppers into 1″ pieces.
Bring 3C water to a boil in a medium pot. Stir in the jasmine rice and 2t salt. Cover and reduce heat to low. Simmer for 10-12 minutes until all the water is absorbed. Keep covered until you are ready to enjoy the meal.
Heat 2T oil in a large sauté pan over high heat until hot and sizzling. Add half of the marinated sliced beef to the pan in a single layer and sear for about 1 minute, flip over and cook for additional 1 minute. Do not overcook sirloin or it will not be as tender. Transfer to a plate and repeat process with the remaining marinated sliced beef.
Add a drizzle of oil to the now empty sauté pan. Heat over high heat. Add broccoli florets and sauté for 30 seconds. Add a splash of water, cover pan, and lower heat to medium. Steam broccoli for about 2 minutes. Remove lid, add white part of green onions, garlic, ginger, and red pepper. Sauté for about 1 additional minute.
Return the cooked sliced beef to the pan with vegetables and toss to combine. Add Mongolian sauce to the pan and cook, stirring constantly, until the sauce is thickened, the beef is cooked, and the vegetables are tender but still crisp.
Plate with rice and garnish with remaining sliced green onion. Serve & enjoy!