Gather all ingredients.
Place chicken breasts on a plate; salt liberally on both sides. Cover loosely with plastic wrap and refrigerate for 1 hour.
Melt butter in a skillet over medium-high heat. Add chicken; cook, turning once, until golden brown on both sides, about 8 minutes. Set aside.
Preheat the oven to 350 degrees F (180 degrees C). Stir soup, sour cream, mushrooms, and garlic powder together in a bowl. Stir in half the cheese.
Spread about half the mixture in the bottom of a casserole dish. Lay chicken breasts on top of cream mixture. Spread remaining cream mixture evenly over chicken. Cover with foil.
Bake in the preheated oven for 30 minutes. Uncover and sprinkle with remaining cheese. Bake until casserole is golden brown and bubbly and chicken is no longer pink at the center, about 10 minutes more. An instant-read thermometer inserted near the center of chicken should read 165 degrees F (74 degrees C) Serve warm.
