Cheddar Brocolli Pasta Bake

16 oz elbow macaroni
1 c milk
1 10.75 oz can Cream of Chicken
1 TBS creamy mustard-mayonnaise blend
1 TBS olive oil
1 sm onion, chopped
2 c shredded cheddar cheese
2 c frozen brocolli

Preheat oven to 350F. Spray 2 qt casserole pan with non-stick cooking spray. Cook pasta according to directions on box; drain and return to pan. Meanwhile, combine milk, Cream of Chicken and mayo-mustard blend in medium bowl. Heat olive oil in saucepan over medium heat; add onion and cook for 2 minutes; add milk mixture and bring to a boil; boil for one minute; remove from heat and stir in 1 1/4 c of the cheddar cheese until smooth. Put the 2 c frozen brocolli in the pan with the macaroni and pour the cheese mixture over it, stirring them together until well combined. Pour mixture into the casserole dish, top with remaining 3/4 c cheese and bake for 20 minutes or until hot and bubbly.