3 tablespoons butter, divided
2 pounds boneless, skinless chicken breast, cut into 1-inch pieces
2 large zucchini, cut into 1/2-inch pieces
1 large red bell pepper, chopped
⅓ cup all-purpose flour
1 cup no-salt-added chicken broth
1 cup whole milk
3 ounces reduced-fat cream cheese
1 ¼ cups shredded part-skim mozzarella cheese, divided
¾ teaspoon ground pepper
½ teaspoon salt