Cook rice according to packet instructions; let cool.
Heat butter in a frying pan over medium-high heat. Add chicken and brown. Season with salt to taste then set chicken aside.
In the same frying pan, scramble the eggs then add the rice, stirring to brown. Add the chicken, mushrooms, spring onions, peas, carrots and soy sauce to taste.
Substitution
You can use 3 1/2 cups of leftover cooked rice if you have some.