1-First Step: Prepare all ingredients by slicing beef sirloin thinly across the grain, washing and slicing bell peppers, and mincing garlic. This mise en place speeds up cooking.

2-Second Step: In a bowl, toss beef slices with cornstarch to lightly coat, which helps thicken the sauce during cooking.

3-Third Step: Heat vegetable oil in a large skillet or wok over medium-high heat. Add beef and sear for 2-3 minutes until browned but not fully cooked; remove and set aside.

4-Fourth Step: In the same pan, add garlic and bell peppers; sauté for 3-4 minutes until peppers soften but remain crisp, preserving nutrients.

5-Fifth Step: Return beef to the pan, add soy sauce and freshly ground black pepper. Stir well and cook for another 2-3 minutes until beef is cooked through and sauce thickens.

6-Final Step: Taste and adjust seasoning if needed. Serve immediately over steamed rice or noodles. To adapt for dietary preferences, swap beef for tofu or seitan, or adjust soy sauce to tamari for gluten-free options.