Drain the feta and place it in a medium bowl. Grind the spices coarsely, if desired. Heat a small skillet over high heat. Add the coriander, cumin, and caraway seeds, and shake the pan continuously until the spices start to release their aroma, about 2 minutes. Immediately transfer to a bowl and pour in the olive oil. Add a pinch of coarse salt. Swirl the spices in the oil and steep for a few minutes. Pour the mixture over the feta. You can even work it in with your hands, gently crumbling the feta, if desired.
Wash and dry the herbs. Trim the stems, but leave them intact. Place the herbs on a large platter in a few fluffy piles. Place the walnuts on the platter, along with the radishes and lavash. Transfer the feta to the platter and garnish it with coarse salt.
For a single serving, pick up a few stalks of herbs. Tear the flatbread into a manageable piece and stuff it with the herbs, walnuts, a small piece of cheese, and a radish or two. Fold and eat like a sandwich.
Note: To remove bitterness from the walnuts, place them in a bowl, add boiling water to cover and a pinch of salt, and soak from 1 hour up to overnight. Before serving, drain and rinse until the water runs clear.
My cookbook The New Persian Kitchen is a winner of Food52's Piglet award. I love cooking Iranian rice and hearing people crunch on the crispy tahdig from the bottom of the pot. I'm passionate about sharing the ingredients and techniques for making Persian food in my writing, cooking classes, and online store, Feast By Louisa where you can find my Persian Spice Set, Tahdig Kit, and other goodies.