Make sure to carefully follow each step of the instructions for the best results :
- Marinate the beef.
Combine the sliced beef with soy sauce, sesame oil, cornstarch, garlic powder, and black pepper in a bowl. Toss well to coat and set aside for at least 10 minutes while you prep the vegetables and sauce. Marinating the beef, even briefly, helps it stay tender and gives it a deeper flavor once it hits the hot pan. - Blanch the broccoli rabe.
Bring a pot of salted water to a boil. Add the broccoli rabe and blanch for 2 to 3 minutes, then drain and immediately plunge into ice water to stop the cooking. Drain well and pat dry. Blanching broccoli rabe before stir-frying softens its bitterness slightly while keeping it vibrant green and tender-crisp in the finished dish. - Mix the stir-fry sauce.
Whisk together the soy sauce, oyster sauce, sesame oil, rice wine vinegar, ginger, garlic, cornstarch, and water in a small bowl until smooth. Having the sauce ready before you start cooking is essential for stir-fry since everything moves quickly once the heat is on. - Sear the beef.
Heat a wok or large skillet over high heat until very hot. Add 1 tablespoon of avocado oil, then add the marinated beef in a single layer. Let it sear undisturbed for about 1 to 2 minutes until browned, then toss and cook for another minute. Remove to a plate. Cooking over high heat and not crowding the beef allows it to sear rather than steam, which gives it the best color and texture. - Stir-fry the vegetables.
Add the remaining tablespoon of oil to the same wok. Add the onion and bell pepper and stir-fry for 2 to 3 minutes until just softened. Add the blanched broccoli rabe and scallions and toss everything together for another 1 to 2 minutes. - Bring it all together.
Return the seared beef to the wok. Pour the stir-fry sauce over everything and toss well to coat. Let the sauce cook for 1 to 2 minutes, stirring constantly, until it thickens and turns glossy. Taste and adjust the seasoning if needed. - Serve immediately.
Divide into bowls and scatter sesame seeds and red pepper flakes over the top. Serve immediately while the beef is tender and the sauce is hot and glossy. This dish is best enjoyed right away over cauliflower rice for a full low carb meal.