Combine garlic, shallot, brown sugar, oil, fish sauce, soy sauce and pepper in large resealable freezer bag. Pierce steaks all over with fork. Add to bag, turning to coat; seal and refrigerate for 8 hours or up to 24 hours.
Discard marinade from meat; pat steaks dry with paper towel. Grill steaks in a closed preheated barbecue over medium-high heat (400°F/200°C) for 6 to 8 minutes for ¾ inch (2 cm) thick steaks, turning twice or more, or until a digital instant-read thermometer inserted sideways into centre of steak reads 145°F (63°C) for medium-rare doneness at the least. Transfer steak to cutting board and let rest for 5 minutes.
Meanwhile, cook vermicelli according to package instructions. Drain and place in shallow bowl or platter; top with lettuce, bean sprouts, mint, cucumber and tomato (if using). Combine water, lime juice, sugar, fish sauce and chile in a small bowl, stirring until sugar is dissolved. Splash sauce over salad and toss to combine.
Cut steaks across the grain into thin slices and serve with Noodle Salad; garnish with peanuts.
Tip: Marinades are all about building steak flavour and juiciness. Piercing steak all over with a fork is what helps tenderize the steak.