Heat the oil in a well-seasoned skillet or nonstick saucepan (I used a dutch oven, so I could puree the sauce right in the pan using my hand blender), and saute the onions, garlic and rosemary on low eat until the onions are soft - about 10 minutes.
Add the tomatoes and half of the chickpeas and cook for another 10 minutes.
Remove the rosemary springs and discard. If you have a hand blender, puree the mixture until smooth. Otherwise, use a blender. Be careful not to burn yourself.
Return the sauce to the pan (if you'd removed it for blending), add the remaining chickpeas, and add salt and pepper to taste.
Meanwhile, cook the pasta.
The original recipe suggests tossing the pasta and sauce together for serving, but we served them separately.
Pass the feta and chopped tomatoes (if desired) at the table.