Cut the chicken breast into bite-sized pieces.
Slice the onion, bell pepper, and paprika into thin strips.
Heat olive oil in a pan, then stir-fry the chicken breast.
When the chicken is half cooked, add the vegetables and stir-fry together.
Add the tomato sauce and simmer for 5 more minutes.
Top with mozzarella cheese, cover the pan, and cook on low heat until the cheese melts.