Saute Onion, Carrot & Garlic: In a large pot, heat the oil over medium heat. When the oil is hot, add the onions and carrots. Season with a pinch of salt and pepper. Cook for 5-7 min, stirring occasionally, until softened. Add garlic and cook for 1 min, stirring often, until fragrant.
Simmer: Add the vegetable stock, chickpeas, orzo and bay leaf. Season with another small pinch of salt and pepper. Bring to a boil then reduce to a simmer over medium-low heat. Simmer for 7-10 minutes, stirring every 1-2 minutes, so the orzo does not stick to the bottom of the pot. Cook until orzo is tender, but still firm to the bite (al dente).
Prepare Sauce: While the soup cooks, add the tahini, lemon juice, miso and warm water to a container and whisk to combine until completely smooth and creamy.
Stir in Sauce, Spinach and Herbs: When the orzo is tender, remove the pot from the heat. Stir in spinach, lemon-tahini mixture and the parsley and dill, reserving a small amount of fresh herbs for serving. Stir for 1-2 min, until spinach is wilted. Season with salt and pepper, to taste.
Serve: Ladle soup into bowls. Sprinkle remaining parsley and dill over top. Serve with a squeeze of fresh lemon, if desired.