Make your chimichurri by adding all ingredients down to Kosher salt to food processor and blending until mixed but still slightly chunky.
With processor running, then drizzle in olive oil until incorporated into sauce.
Using 1/4 cup of the chimichurri, rub sauce into both sides of your meat and let sit at room temperature for 1/2 hour. (Reserve additional chimichurri for serving.)
Preheat oven to 450 degrees.
When oven comes to temperature, place your meat in aroasting pan with a rack
Turn oven to broil and roast for four minutes a side, keeping oven door cracked open.
Let your cooked London Broil sit for 10 minutes before slicing against the grain.
Serve with the rest of your chimichurri sauce.
Tip: Just close the oven door on an oven mitt to keep it slightly cracked. Four minutes a side on these thicker pieces gives you some medium rare London Broil, but since this is a tougher cut of meat, I prefer mine both marinated and on the rarer side. Broil yours a little longer if you don't like it as rare, but realize it will have a tendency to toughen up when it's more well done.
Chimichurri London Broil from Mashup Mom: https://www.mashupmom.com/chimichurri-london-broil/