Follow these simple steps to create your Thai Beef Salad:

1. Prepare the Beef: Season the flank steak or sirloin with salt and pepper.
2. Cook the Beef: Heat a grill or skillet over medium-high heat. Cook the beef for about 4-5 minutes on each side, or until it reaches your desired level of doneness. Remove from heat and let it rest for a few minutes.
3. Slice the Beef: Once rested, slice the beef thinly against the grain to ensure tenderness.
4. Mix the Dressing: In a small bowl, whisk together fish sauce, lime juice, sugar, and chili flakes (if using) until the sugar dissolves.
5. Combine the Vegetables: In a large bowl, combine the mixed salad greens, cherry tomatoes, cucumber, bell pepper, red onion, cilantro, and mint.
6. Add the Beef: Place the sliced beef on top of the vegetable mixture.
7. Dress the Salad: Drizzle the prepared dressing over the salad and toss gently to combine all the ingredients.
8. Taste and Adjust: Taste the salad and adjust seasoning with additional salt, pepper, or lime juice as needed.
9. Plate the Salad: Serve immediately for the freshest taste.

These straightforward steps will guide you in creating a delectable Thai Beef Salad that will impress your family and friends.