Place the birds eye chili, garlic, cilantro stems and a small pinch of salt into a mortar and pestle. Grind until a smooth paste forms.
Add the remaining Dressing ingredients. Adjust sugar, lime juice and fish sauce to taste. Set aside.
Drizzle the beef with ½ tbsp of oil on both sides, then sprinkle with a good pinch of salt and pepper.
Preheat a skillet over high heat until screaming hot and smoking. Cook the beef to your liking - rare is preferred for this salad.
Remove the beef from the skillet onto a plate. Loosely tent with foil and set aside for 10 minutes to rest.
Slice the beef thinly against the grain and place in a bowl with the remaining Salad ingredients.
Pour over Dressing and toss gently.