In food processor, (I used my blender), chop together onions, cilantro, parsley, jalapeno peppers and 1/2 cup water; transfer to a bowl, stir in oil, vinegar, garlic and salt. Make it as smooth or chunky as you prefer, we like ours chunky.
In a large shallow dish or zip lock bag, spoon half of the pebre over the steak; turn to coat; cover and refrigerate steak and remaining pebre separately for at least 4 hours or up to 24 hours.
Discard the marinade and place the steak on a veggie sprayed grill over medium high heat, close lid and grill turning once until desired doneness, about 10 minutes for medium rare.
Transfer to cutting board and tent with foil, let stand for 5 minutes before slicing thinly across the grain.
Stir the tomatoes into the remaining pebre and serve with the steak.
Alternately; I grill my steak on a veggie oil sprayed griddler, close lid and grill for no more than 5 minutes for medium rare.