In a pot, warm olive oil over medium heat. Add sausage and cook, stirring, until browned all over, about 5 minutes. Transfer to a paper towel-lined plate. Discard all but 1 Tbsp. of fat from pot. Add onion and garlic, and cook, stirring often, until soft, about 3 minutes.
Return sausage to pot and add chicken broth, 3 cups water and beans. Bring to a boil, reduce heat to low and simmer for 15 minutes. Stir in spinach until wilted, 1 to 2 minutes. Season with salt and pepper and serve hot.