Use a different bread - whole wheat would be best, but if you don't like the taste of it, potato bread is good too. Instead of mayonnaise, use either butter or try tomato paste (it's rather good) and along with your turkey, add some slices of cheese too. Prepare a salad to go along with your sandwich and you have a healthy lunch.
If your parents don't allow you to touch the oven then use oatmeal for breakfast. You can heat it in the microwave with either water or milk.
Add some raspberries or blueberries to it and you have a great breakfast
and you won't get hungry right away again.
Don't forget to snack after 2 to 2.5 hours though.....that's important, as
it keeps your metabolism busy and you won't get too hungry for your next meal.