For best results, use high-quality extra virgin olive oil. Its fruity flavor will enhance the chimichurri. Adjust the amount of red pepper flakes to control the heat level. Start with 1 tablespoon and add more to taste. Don't overcook the shrimp, as they will become rubbery. They are done when they turn pink and opaque. Leftover chimichurri sauce can be stored in an airtight container in the refrigerator for up to 3 days. It's also delicious on grilled meats, vegetables, and fish.