Cook bacon in a large pot over medium-high heat until the fat has rendered out and the bacon begins to crisp. Pour out the excess grease, then stir in the onion. Continue cooking and stirring until the onion has turned golden-brown, 5 to 8 minutes more. Add the salmon cubes, and cook gently until they turn opaque on all sides, but are not yet cooked in the center.

Increase heat to high, and pour in the chicken broth. Once the soup begins to simmer, reduce heat to medium-low, and cook for 10 minutes. Stir in the spinach and garbanzo beans, return to a simmer, then season to taste with salt and pepper, and serve.