Bring a large pot of salted water to a boil. Add the cheese tortellini and cook according to package instructions until al dente (usually 3-5 minutes). Drain and set aside.
In a mixing bowl, combine softened cream cheese, ranch dressing, milk, garlic powder, onion powder, salt, and pepper. Whisk until smooth and creamy.
Add the cooked shredded chicken to the sauce mixture and stir to coat evenly.
Preheat your oven to 375°F (190°C). In your baking dish, add the cooked tortellini, then pour the creamy chicken ranch mixture over the top. Gently fold everything together so the tortellini is evenly coated.
Sprinkle the shredded cheddar and mozzarella evenly over the top of the casserole.
Place the baking dish in the oven and bake for 20-25 minutes, or until the cheese is melted, bubbly, and starts to turn golden brown.
Remove from the oven and let it cool slightly. Sprinkle chopped green onions on top for freshness and a pop of color. Serve warm and enjoy!