Slice the onion, cut the garlic clove in half. Fry in olive oil together, after approx. 1 minute add the chicken to the pan and fry for 2 more minutes per side.
Take the chicken and the garlic out of the pan and set aside. Add tomato sauce to the pan, season with salt, pepper and oregano and simmer for approx. 5 minutes.
Put the chicken back into the sauce, simmer for 5 more minutes or until cooked through.
Slice the mozzarella and put the slices on top of the chicken breasts. Cover the pan with a lid and let the mozzarella melt for 1–2 minutes.
Tipps
Add some chili powder if you want the sauce to be spicy too!