For the steak:
Combine all ingredients, and let steak marinate, refrigerated, for 1 to 3 hours.
Heat grill or pan to high heat, cook skirt steak to medium-rare, let sit for 5 to 10 minutes, then cut on bias in 1/4 inch pieces, and top with chimichuri sauce.
Mix all ingredients lightly in food processor until a coarse sauce is formed. Set aside for 2 hours.