This is a very simple version of the ubiquitous Argentinian this condiment. You can use this right away (it only takes 10 minutes to throw together), but the flavors are much better if you let it sit for at least a day so that the oil can absorb the flavors from the garlic, onion, and parsley.
2 cups olive oil
2 tbsp. vinegar (your favorite)
1/2 onion, minced
3 garlic cloves, minced
Several parsley sprigs, minced
Salt and freshly ground black pepper to taste
Mix ingredients well in a covered jar. Serve at room temperature over grilled meat.