-As the rashteh sits, the pasta absorbs the liquid and it gets thicker. That is not a bad thing, but if you prefer a soupier rashteh, add in a splash of water to make it runnier.
-Swiss chard, kale, or bok choy all make good substitutes for the spinach. You would need to add those earlier to the cooking, since they all take a bit longer to cook down than the spinach.
-You can easily make this gluten-free by substituting your favorite gluten-free pasta.
-The herbs are up to you, I've made this with parsley, cilantro, and mint. A combination of two of them would be great, too.