These two sauces are actually quite different. First, pesto is an Italian sauce, while chimichurri is Argentine. Second, chimichurri is a blend of finely chopped parsley and oregano, while traditional pesto is made with lots of basil. Third, pesto calls for olive oil to bind all the ingredients, while chimichurri adds red or white wine vinegar for that signature puckery tang aside from a little olive oil.