Preheat oven to 350 degrees then coat a 2-qt casserole dish with cooking spray. Place a large skillet over medium-high heat then add butter and onion. Cook 3–4 minutes until onions are softened and translucent then add garlic and cook an additional 30 seconds.

Sprinkle flour over onion mixture then stir to combine. Cook flour for 30 seconds, stirring constantly then stir in warm milk. Add chicken bouillon, pepper and Italian seasoning. Blend and stir to combine. Bring mixture to a boil then reduce heat to medium-low and simmer for 5 minutes.

Remove sauce from heat then stir in sour cream, uncooked rice, vegetables, shredded cheese and shredded chicken. Stir to combine then transfer mixture to prepared casserole dish.

Cover casserole dish with foil and bake for 45 minutes. Remove from oven, give the casserole a gentle stir then cover the top with crumbled baked potato chips. Return the casserole to the oven and cook uncovered for an additional 15 minutes.

Remove from oven and allow it to rest for 10 minutes to set up and cool a bit before serving.