In a large bowl, combine 1½ pounds sliced beef, 1 tablespoon sesame oil, 1 tablespoon cornstarch, ¼ cup soy sauce, 1 tablespoon dark soy sauce, 1 tablespoon oyster sauce, 1 tablespoon brown sugar, and 4 minced garlic cloves. Toss well and let marinate for 10 minutes.
Heat 2 tablespoons peanut oil in a large skillet or wok over medium-high heat. Add the marinated beef in a single layer and sear for 2 to 3 minutes per side, until browned and sticky. Work in batches if needed so the beef actually sears instead of steams. Remove the beef from the pan and set aside.
In the same pan, add the sliced onion, red bell pepper, broccoli, julienned carrots, and the white parts of the green onions. Cook for 3 to 4 minutes, stirring often, until the vegetables are just tender but still have some bite.
Add 4 cups cooked day old rice to the pan and stir to combine with the vegetables. Let the rice sit undisturbed for 1 to 2 minutes so it can get a little toasty.
Return the beef to the pan. Add 2 tablespoons hoisin sauce, 1 tablespoon soy sauce, 1 teaspoon dark soy sauce, and 1 to 2 teaspoons sriracha. Toss everything together until well coated and glossy.
Taste and decide if it needs 1 teaspoon brown sugar. Add it only if you want that extra sticky sweet finish.
Remove from heat and garnish with the green parts of the green onions. Serve hot.