Cook white rice as per directions on the box.
Sauté diced onions until slightly see through, then add your corn and peas. You may need to add more butter at this point. Cook on low until corn and peas are warmed through. Sir often and add butter as needed to prevent browning. If you're going to use meat, cut into bite size pieces and add to veggies at this point until meat is hot.
When your rice is cooked, add your veggie mixture to your rice pot. Make sure any butter in the pan is also added to your rice. Stir until well mixed. Add soy sauce to taste.