Mix lemon juice, butter, and minced garlic and place in 13x9 baking dish. Add chicken and bake for 20-30 minutes until no longer pink inside chicken pieces. (Turn chicken once about 15 minutes into cooking time.).
While chicken is baking, cut sourdough bread into bite-sized pieces and slice mozzarella cheese.
When chicken is done, cut it into bite-sized pieces. Pour lemon/butter/garlic juice into a measuring cup.
Put bread slices into baking dish, top it with chicken pieces and then mozzarella cheese slices enough to cover the top. Drizzle 1/2 cup or more of lemon/butter/garlic over the top, and then bake for another 15-20 minutes.