The best ways for your diet to boost your metabolism is to eat 5-7 meals per day, with a serving of protein with each.
Oatmeal is perfect for breakfast, but only if it's old-fashioned oats and not the instant kind (they're full of sugar and other added ingredients). You should definitely have some protein at breakfast, too - chicken, egg whites, etc.
Lunch - you should certainly bring your own; school lunches are never well-balanced nor clean. I would suggest making a tuna salad (w/ lemon juice instead of mayo) or some grilled chicken. And have some fruit, too, or a salad - to get in a serving of fresh produce. If you like sandwiches, be sure it's 100% stone-ground whole wheat bread - otherwise you're better off w/o it.
You ought to try to have a snack while at school - some protein and something else - maybe some grilled chicken breast and a serving of walnuts or almonds, and some fruit. Since you're in school, perhaps you can eat during study hall? Or quickly between classes in the halls?
As for supper, just be smart about what you're eating - eat modest portions, and try to choose healthy foods.
And don't forget another meal after that - cottage cheese seems to be a favourite, and it's perfect for before bed (it's casein protein, which helps prevent the body going catabolic while sleeping).
If you do a search on these forums for clean diets and such, you'll find similar, and perhaps more detailed, information.
