"Pantry Raid" Chicken Enchilada Casserole

INGREDIENTS

• 1 (15 ounce) can tomato sauce
• 1/4 cup water
• 1 envelope taco seasoning mix
• 1 1/2 tablespoons chili powder
• 1 tablespoon vegetable oil
• 1 pound chicken breast tenderloins
• 1 (15 ounce) can black beans, drained
• 1/4 cup cream cheese
• 1 cup shredded Mexican-style cheese blend, or more to taste
• 1 (7.5 ounce) package corn bread mix
• 1 egg
• 1/3 cup milk