Marinade:
1/4 cup chopped cilantro leaves and stems
8 garlic cloves
1/2 serrano pepper, seeded
2 tablespoons fish sauce
2 tablespoons lime juice (about 2 limes)
1/2 cup oil, plus more for cooking steak
1 pound sirloin steak
Dressing:
1/4 cup fish sauce
1/4 cup lime juice (about 4 limes)
1/4 cup chopped cilantro leaves and stems
1 tablespoon brown sugar
1/2 serrano pepper, seeded
Salad:
5 ounces butter lettuce
1 cup halved cherry tomatoes
1 cup chopped cucumber
1/2 red onion, thinly sliced
1/4 cup chopped mint leaves
1/4 cup chopped cilantro leaves and stems
Combine marinade ingredients in a food processor and process until smooth. Place steak in a baking dish. Pour marinade over steak and turn steak to coat. Let stand at room temperature for 30 minutes. Make dressing: Combine ingredients in a food processor and process until sugar is dissolved, about 30 seconds. Heat 2 tablespoons oil in a large skillet over medium-high heat. Sear steaks 4 minutes on each side for medium-rare. Let steak rest 10 minutes, then slice against the grain. Combine salad ingredients in a large bowl. Pour dressing over and toss, then top with steak slices. Toss again and serve immediately.