Cook mushrooms over medium high heat in a large skillet, stirring to prevent burning. Add flour, stirring well. Then gradually add water, frozen orange juice concentrate, onions and chicken bouillon powder or cubes. Bring to a boil, reduce heat and add chicken, simmering uncovered for 3-4 minutes.
Cool and pour into freezer containers.
On cooking day
On cooking day, thaw orange chicken mixture.
Heat chicken in a saucepan until heated through and bubbly, then add mandarin oranges, continuing to heat mixture. Add to cooked rice and serve.