Heat olive oil in a stock pot over moderate heat.
Add the minced garlic and onions. Stir often to prevent browning the garlic.
When the garlic is fragrant and the onions are slightly translucent (approx. 3 minutes), add 2 cups of the cooked chickpeas; reserve the last cup for later.
Add the raw baby spinach.
Finally, add the kosher salt, ground black pepper, onion powder, and dill.
Stir well, and allow to simmer until the spinach is mostly wilted. Add more olive oil if the stock pot seems dry.
Once the spinach is wilted, add the vegetable stock, milk, the dill pickle brine, diced dill pickles, and Dijon mustard.
Bring to a simmer and allow to simmer for approx. 10 minutes.
Remove the stock pot from the heat.
Carefully transfer the contents of the stock pot to a blender or food processor. You can do this in batches if you must. If using an immersion blender, then just turn down the heat and blend in the stock pot.
Blend until your soup is a smooth puree.
Add the plain Greek yogurt and blend again until smooth.
This is where you want to do a taste test. Add seasoning if you need to.
Carefully transfer the puree back to the stock pot and bring to a low simmer.
Add the remaining chickpeas.
Let the soup simmer for approx 15 minutes. It will thicken. If it doesn't thicken to your preference, add more plain Greek yogurt; stir well to ensure it's thoroughly mixed.
Serve and garnish with chopped fresh dill or dry dill, a few croutons, an olive oil drizzle...whatever your heart desires!