Preheat the oven to 375 degrees F (190 degrees C).

Mix vegetables, condensed soup, water, rice, and onion powder together in a 12x8-inch shallow baking dish. Arrange chicken breasts on top; cover.

Bake in the preheated oven until chicken is no longer pink and cooked through, about 45 minutes. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C). Top with shredded cheese and serve.