Use a meat tenderizer on the steaks, pounding both sides. Sprinkle with rub and a dusting of garlic powder. Put in bag with marinade, tossing to coat. Place in fridge for the day or overnight.
Mix the pesto about an hour before using, salting to taste and adding just enough olive oil to make paste.
Take steaks out of marinade about an hour before bbqing, giving a good coating of pesto on both sides (do so about an hour before bbq'ing to bring up to room temperature).
Grill steaks to desired doneness!