Preheat oven to 400ºF.

In a large bowl mix together spinach, yogurt, artichokes, garlic powder, and mustard.

Lay chicken breasts down in a single layer in a 9x13 baking dish. Evenly distribute spinach mixture overtop the chicken breasts. Lay 2 slices of the mozzarella cheese on top of each chicken breast, overlapping to fit is okay.

Transfer to the oven and bake 30 minutes until chicken is fully cooked (cooking time will vary due to size of the chicken breast, the chicken should reach an internal temperature of 165ºF). Let rest 3-5 minutes before serving.