Drizzle flap steak with olive oil and season with salt and pepper. Let sit for 30 minutes while you prepare the salad and heat up the barbecue.
Whisk together all the vinaigrette ingredients and set aside.
In a salad bowl or on a large platter, add the lettuces and red onion.
Barbecue steak until medium rare; let rest and then slice.
Add steak to salad mix and toss together with dressing.
Serve with a baguette and grilled lemon. Enjoy!