I can tell you what I do, but just a warning -- I tend to have more carbs than the average person and I don't really care. I was raised on carbs and I'm fine with them. I also am not as much a fanatic as some are about healthy eating. I try to cut out fat whenever I can, but I don't do things like health shakes or meal supplements. Eating is fun for me and as long as I work out and don't have food-related health problems, I don't see why I shouldn't enjoy what I eat.
Now, how big is your freezer? What I do is stock up on all kinds of foods because I have a huge freezer. So on Saturday, I do the slow cooker. Do you have one? If not, get one. I basically put in 10 chicken breasts, a bag of baby carrots, some potatoes I cut up, and some celery. I dump it all into the slow cooker, hit 5-6 hours, and leave it. After that time, I've got 10 meals ready to be transferred to containers and stored in the freezer. Rice takes 10 minutes to cook, so when I get home from school, I make some rice and warm up one of the chicken meals to go with it.
I also make a huge pot of chili with ground turkey. Chili is the easiest thing to make and if you do it with turkey instead of beef, it's not bad for you. I do turkey, tomatoes, red peppers, sauce, chili powder, and beans. I make enough for about 7 days or so. I freeze it. When it's time to eat, I warm it up and toast 3-4 slices of bread (gotta have my carbs!), and enjoy.
The other thing I like may seem a little odd to some, but I like it. I use ground turkey and cook it up (drain the fat), add your spices, etc., then cook rice right there in the same pot with the turkey. It gives the rice the turkey flavor and in the end, I've got some rice/turkey concoction which I like. Again, I make enough for about a week and freeze.
I also freeze ground turkey cooked up with pasta sauce. I then cook some spaghetti or whatever during the week and there you go, a pasta meal.
Chicken casserole can be easy if you want to buy store-bought chicken strips. I make it with rice. Just cook up the rice, transfer it to a glass pan that can go in the oven, add some broccoli, throw in the chicken, sprinkle some cheese, and pop it into the oven for about 30 minutes. If it's a big pan, you can make enough for about 7-10 days. Freeze.
For breakfast, I like cereal, oatmeal, and chicken salad (yes, I know it's not really breakfast food) with cucumbers, lettuce, carrots, green peppers, olive oil, and lemon juice, and the chicken of course. I also like eggs and potatoes. I cook my potatoes with a bit of garlic and paprika and enjoy it. Sometimes I go through a phase where I have to have eggs every day, so I use egg beaters instead of real eggs. Tastes the same to me.
For lunch, I'll generally take a sandwich with me -- turkey, ham and cheese, whatever, or I'll take leftovers from dinner or anything in the freezer I need to get rid of to make room for whatever I plan to cook and store that weekend. I also take carrots or apples (apples and cheese -- favorite!) or grapes. I sometimes make pasta salad (no mayo since I'm not a fan of it) and take it with me (make sure you have a fridge/microwave at school). I need some chocolate by mid-day, so that's when I generally bring a few chocolate chip cookies or I buy a bag of Hershey's kisses and stuff 5-6 kisses in my lunch bag each day. I'm also a chip eater, so I sometimes do the vending machine thing, but I don't allow myself to keep chips in the house since I know I could go through a giant bag in no time. I usually use lunch for my snacks and don't usually deprive myself of one snacky item.
Anyway, hope this gives you a few ideas. It really isn't difficult to eat three meals a day in med school, so long as you plan ahead. Don't expect to come home from school at 5 p.m., have four hours of studying ahead of you, and think you're going to cook a steak that night. Cook on the weekends, freeze your meals, and do light cooking on the weekdays -- rice, pasta, easy fixes.