In a bowl, whisk together the soy sauce, fish sauce, sugar, minced garlic, and black pepper to create the marinade.
Add the thinly sliced beef to the marinade, ensuring each slice is well-coated. Let it marinate for at least 30 minutes.
While the beef is marinating, prepare the fresh herbs, red onion, cucumber, and red chilies.
Heat a grill or skillet over medium-high heat. Grill the marinated beef slices for 1-2 minutes on each side or until cooked to your liking.
In a mixing bowl, combine the grilled beef, fresh herbs, red onion, cucumber, and red chilies.
Pour the freshly squeezed lime juice over the salad and toss gently to combine all the flavors.