Heat the oil in a medium saucepan. Add onion, cook and stir until softened (about 5 min). Add garlic, cook and stir for 1 minute. Stir in chickpeas, sage, and pepper.
Stir in the broth, spinach, and salt; bring to a boil. Use an immersion blender to puree (or transfer to a food processor and puree). Simmer for 5 minutes after pureeing. Stir in lemon juice.