This is particularly good with shrimp skewers or short ribs, but it would be at home with any simple fish steak or fish fillet off the grill. I went with a straightforward white wine vinegar here, but you can fine tune this to your own taste by using sherry vinegar, lemon and/or lime juice, or balsamic vinegar.
Pour the oil into a blender jar. Add the cilantro, parsley, almonds, and vinegar and blend until the herbs are finely chopped and the mixture is fairly smooth. Season, to taste, with salt and pepper. The pesto can be made up to a day in advance. Scrape into a storage container and press a piece of plastic wrap directly on the surface to prevent the pesto from turning dark. Refrigerate until ready to use. Bring the pesto to room temperature before serving.