Speedy Ziti With Zesty Chicken

• 1 onion (chopped)
• 280 gr pa peas defrosted (frozen)
• 475 ml low-sodium chicken broth
• 200 gr ziti
• 200 gr chicken (cooked chopped)
• 60 ml lemon juice
• 16 gr all purpose flour
• 16 ml dijon mustard
• 9 gr butter
• 7 gr parsley (fresh chopped)