Sausage and White Bean Ragout

1 tablespoon olive oil
1/2 cup chopped onion
2 (4-ounce) links chicken sausage, cut into (1/2-inch) slices
1 zucchini, quartered and cut into (1/2-inch) slices (about 2 cups)
3 garlic cloves, peeled and crushed
6 cups chopped trimmed kale (about 1/2 pound)
1/2 cup water
2 (16-ounce) cans cannellini beans or other white beans, rinsed and drained
1 (14.5-ounce) can diced tomatoes, undrained
1/4 teaspoon salt
1/4 teaspoon freshly ground black pepper

Heat oil in a large skillet over medium-high heat. Sauté onion and sausage 4 minutes or until sausage is browned. Add zucchini and garlic; cook 2 minutes. Add kale and remaining ingredients; bring to a boil. Cover, reduce heat, and simmer 10 minutes or until thoroughly heated. Serve immediately.