Step 1: Season the Chicken - Place the cubed chicken breasts in the bottom of your slow cooker, spreading them out so they are not piled too high in one spot. Sprinkle the salt, pepper, and garlic powder evenly over the chicken. I like to season the chicken first because it means every bite has flavor, not just the sauce around it. Think of this as building the foundation of the whole dinner.
Step 2: Add the Onions and Butter - Scatter the thinly sliced onions over the chicken, then dot the butter over the top. The onions are going to cook low and slow, softening into the sauce and bringing that French onion flavor we are after. You do not need to brown them first, which is one of the reasons I like this recipe so much. The slow cooker handles the job while you go about your day.
Step 3: Whisk the French Onion Sauce - In a mixing bowl, whisk together the French onion soup, brown gravy mix, beef broth, Worcestershire sauce, and minced garlic until the gravy mix is mostly dissolved and the sauce looks smooth. This mixture is where all that deep, savory flavor comes from. The beef broth and French onion soup make it taste rich, while the Worcestershire sauce gives it that little something you cannot quite name but would miss if it were gone.
Step 4: Pour the Sauce Over Everything - Pour the sauce evenly over the chicken and onions. Try to cover as much of the chicken as you can so everything cooks in that savory onion gravy. Do not stir too much at this point. Just let the sauce settle down into the chicken and onions. The slow cooker will bring everything together as it cooks.
Step 5: Cook Until the Chicken Is Tender - Cover the slow cooker and cook on low for 5 to 6 hours or on high for 3 to 4 hours, until the chicken is tender and cooked through. I usually prefer low when I have the time because the chicken stays nice and tender. When it is done, the onions should be soft, the sauce should smell amazing, and the chicken should be easy to cut with a spoon.
Step 6: Stir in the Creamy Ingredients - Add the softened cream cheese and sour cream to the slow cooker, then stir until the sauce becomes smooth and creamy. Take your time here. Cream cheese can be a little stubborn if it is cold, so softened cream cheese really does help. Once it melts in, the sauce turns into this rich, creamy French onion gravy that coats everything beautifully.
Step 7: Add the Tortellini and Half the Cheese - Add the frozen cheese tortellini and half of the shredded cheese, then stir gently so the tortellini gets coated in the sauce. Be gentle here because tortellini can tear if you get too aggressive. The goal is to tuck it into that creamy sauce so it can cook through without getting mushy. This is the moment when the recipe turns from chicken and gravy into a full cozy pasta dinner.
Step 8: Top with the Remaining Cheese - Sprinkle the remaining shredded cheese evenly over the top. This creates that melty, cheesy layer that makes the whole slow cooker look like something you want to dive into with a big spoon. Swiss, Gruyere, Gouda, mozzarella, or an Italian blend all work, so use what your family likes best.
Step 9: Finish Cooking Until Melty - Cover the slow cooker again and cook on high for another 20 to 30 minutes, until the tortellini is tender and the cheese on top is melted. Keep an eye on it near the end because tortellini cooks pretty quickly once the sauce is hot. When it is ready, sprinkle with chopped parsley and serve it warm.