Preparing the bulgur/quinoa: If using bulgur, pour boiling water over it, cover, and let it sit for about 30 minutes until it is tender. If all the water is not absorbed, drain the bulgur using a strainer. If using quinoa, cook it according to the package instructions, then let it cool.
Chopping herbs and vegetables: While the bulgur or quinoa is cooling, finely chop the parsley, mint, tomatoes, cucumber (if used), and onion.
Mixing: In a large bowl, mix the cooled bulgur or quinoa with the chopped herbs and vegetables.
Seasoning: Add the lemon juice and olive oil. Season with salt and pepper to your taste.
Refrigeration: Let the tabbouleh rest in the refrigerator for at least an hour before serving. This allows the flavors to blend and intensify.
Serving: Serve the tabbouleh chilled, as a refreshing and aromatic salad.