Toss chicken with dried parsley, garlic powder, onion powder, salt and pepper in a medium bowl until evenly coated.
Heat oil in a large skillet over medium-high heat. Add the chicken in a single layer; cook, stirring occasionally, until golden, about 5 minutes. Add 1 ½ cups milk and broth; bring to a simmer. Add pasta and cook, stirring occasionally, until just tender (checking timing on your pasta package), adding broccoli during the last 3 minutes of cooking time.
Meanwhile, whisk flour and the remaining ¼ cup milk in a small bowl. When the pasta is tender, stir in the flour mixture. Cook, stirring occasionally, until thickened. Remove from heat.
Add 1 cup cheese and Buffalo sauce; stir until the cheese is melted. Sprinkle with the remaining ¼ cup cheese. Garnish with parsley, if desired.
