Combine the garlic, the 1/4 cup cilantro leaves, olive oil, and 1/2 teaspoon freshly ground black pepper in the bowl of a food processor. Pulse until everything is chopped and combined. Spread evenly over the steak.
Heat a wok or skillet and spray with the cooking spray. Add the steak and cook about 4 min. on each side. Remove the steak and set aside to cool.
To make the dressing, combine the fish sauce, the fresh lime juice, the soy sauce, chili pepper, and brown sugar in a bowl and whisk until sugar is dissolved.
Slice the steak into thin strips. Place the lettuce on a plate and add the tomatoes, cucumbers, scallions, and the steak. Drizzle the dressing on top and top with more fresh Cilantro leaves.