Colorful Three-Bean Soup Recipe

1 medium onion, chopped 1 tablespoon canola oil 3 small potatoes, peeled and cubed 2 medium carrots, sliced 3 cans (14-1/2 ounces each) chicken or vegetable broth 3 cups water 2 tablespoons dried parsley flakes 2 teaspoons dried basil 1 teaspoon dried oregano 1 garlic clove, minced 1/2 teaspoon pepper 1 can (15-1/2 ounces) great northern beans, rinsed and drained 1 can (15 ounces) pinto beans, rinsed and drained 1 can (15 ounces) garbanzo beans or chickpeas, rinsed and drained 3 cups chopped fresh spinach