Sauté aromatics: In a heavy pot or Dutch oven, heat olive oil over medium heat until shimmering. Add onions, celery, carrots, and (optional) Calabrian chili paste. Sauté for 3-5 minutes, until onions are translucent. Add in minced garlic and sauté for another minute.
Build the soup: Add in vegetable broth, chickpeas, dried oregano, and bay leaf. Bring the mixture up to a boil
Cook the pasta: Stir in the dry orzo. Reduce heat to medium-low to establish a rapid simmer. Simmer for 7-10 minutes, or until orzo is almost al dente. Then stir in your baby spinach and allow to simmer for another 2-3 minutes, until greens are wilted and pasta is cooked. (Heartier greens such as Tuscan kale require more cook time. I recommend adding them in at the same time as the pasta.)
Add herbs and lemon: Stir in the fresh herbs (parsley and/or dill), along with the fresh lemon juice and the (optional) lemon zest.
Thicken (optional): In a small bowl, whisk together tahini with 4 tablespoons cold water until fluffy and pourable. Add extra water 1 tablespoon at a time as needed. Stir this into the soup and allow it to simmer for another minute.