Simmer chickpeas in water to cover by 2 inches in a large pot, partially covered with lid, adding more water if necessary, until tender, 1 to 1 1/4 hours. 

 

Meanwhile, bring a large pot of salted water to boil. Cook pasta until al dente. Reserving 3⁄4 cup of the pasta cooking liquid, drain pasta. Transfer pasta to a large bowl. 

 

Drain chickpeas. In a blender, purée 2 cups chickpeas with the vegetable broth until smooth. Transfer chickpea sauce to a large pot.  

 

In a large skillet, heat oil over medium-high heat; remove pan from heat. Add rosemary, garlic and pinch salt; swirl to combine. Add fish, return pan to medium-high heat and cook, stirring occasionally, until fish is just cooked through, 1 to 2 minutes; season with salt. 

 

Add pasta to chickpea sauce; add 1/2  to 3⁄4 cup of the pasta cooking liquid to thin sauce; stir to combine. Cook over medium heat, until just warmed through; remove from heat. Gently stir in fish and oil from pan; season with salt.

 

Transfer pasta to serving plates. Top with remaining whole chickpeas. Drizzle with oil, season with pepper and serve immediately.