Place the chicken in a saucepan and add water to cover. Bring to a boil over high heat, then reduce the heat to medium-low, cover, and simmer until the chicken pieces are no longer pink, about 10 minutes.
Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking dish.
Melt the butter in a skillet over medium heat. Stir in the mushrooms; cook and stir until the mushrooms are lightly browned and have released their liquid, about 5 minutes.
Place the chicken pieces in the prepared baking dish and add the sauteed mushrooms.
In a small saucepan over medium heat, combine and heat the soup, milk, Cheddar cheese and garlic powder. Remove from heat and add the white wine and mayonnaise. Pour mixture over the chicken and mushrooms. Top with slivered almonds and grated Parmesan cheese and bake in the preheated oven for 1 hour.