Heat olive oil in a large frying pan on high heat.
Add chicken and onion and cook until onion is tender and chicken is browned and cooked through About 8-10 minutes.
Add garlic and cook a further 30 seconds.
Reduce heat to medium low and add spinach and lemon zest. Cover the pan and cook until spinach wilts (about 2-3 minutes).
Reduce heat to low and add thickened cream, cream cheese, parmesan cheese & mozarella cheese. Stir to combine until all of the cheese is melted. The cream cheese will take the longest.
Add cooked penne pasta and stir to mix through the creamy sauce. Serve immediately.