Combine chilli, sweet chilli sauce, garlic, soy sauce and half of the fresh herbs together for the beef marinade and place in a shallow dish. Add the beef and roll the piece of beef fillet until thoroughly coated in the ingredients. Cover and chill in the fridge for 1 hour.
Preheat a griddle pan, grill or barbecue and cook on a medium heat for about 15-20 minutes turning frequently until browned on the outside and pink and juicy in the centre.
Combine all the remaining ingredients for the relish.
Allow the steak to rest for 5-10 minutes and then slice thickly.
Serve with the peanut relish and noodle salad.