Preheat a barbecue or griddle pan to hot. Season the steak with lots of black pepper, drizzle with oil and place onto a hot barbecue or griddle pan for five minutes, turning half-way through.
To make the dressing, put the chili, palm sugar, garlic infused oil and a teaspoon of salt into a pestle and mortar.
Grind for 1-2 minutes, then add the coriander and mint and grind for another minute. Mix in the fish sauce, soy sauce, lime juice and zest.
Cut the lettuce into six wedges and place in a bowl. Top with the tomatoes, radishes and a few coriander leaves. Pour the dressing over the salad and toss to coat. Slice the beef and lay it on top of the salad.