Prepare the Marinade/Dressing: In a measuring cup, combine the fish sauce, lime zest and juice, orange juice, garlic, brown sugar, and minced chile. Reserve half the mixture for the noodle salad dressing.
Marinate the Steak: Place the skirt steak in a shallow bowl or a heavy-duty sealable plastic bag. Pour the remaining marinade over the steak, ensuring it is fully coated. Cover and refrigerate for at least 30 minutes or up to 12 hours.
Cook the Steak: Heat a grill or broiler to high. Remove the steak from the marinade, pat off excess liquid, and cook over direct heat or under the broiler. Grill 2 to 4 minutes per side for rare, adjusting to your preferred doneness. Let the steak rest, lightly covered with aluminum foil, for 10 minutes before slicing.
Assemble the Salad: In a large bowl, toss the cooked rice noodles, cucumbers, radishes, mint leaves, and peanuts with the reserved marinade. Slice the steak thinly across the grain.
Serve: Divide the noodle salad among individual plates and top each serving with slices of steak. Garnish with additional mint leaves if desired.