Start by heating the olive oil in a large pot over medium heat. Add the diced onion, carrots, and celery. Sauté these vegetables for about 5-7 minutes, or until they become soft and fragrant.
Once the vegetables are softened, add the minced garlic and cook for an additional minute. Then, add the Italian turkey sausage to the pot. Break it up with your spoon as it cooks, allowing it to brown evenly for about 5-6 minutes.
After the sausage has browned, stir in the diced tomatoes along with their juices. Sprinkle in the Italian seasoning and red chili flakes (if using). Give it a good stir to combine all the flavors.
Next, pour in the chicken broth and bring the mixture to a boil. Once boiling, reduce the heat to low and let it simmer for about 20 minutes.
Stir in the cannellini beans and the chopped kale. Simmer for an additional 5-10 minutes, or until the kale is tender but still vibrant in color.
Once the kale is cooked, taste the soup and adjust any seasonings if necessary. Ladle the soup into bowls and enjoy it warm.