This is pretty easy and you can put whatever you want in the stuffing so...

1.5 lb of flank steak
16 oz spinach (1 large bag is ok also I just liek a lot)
1 14.5 oz can of diced tomato (or chop your own)
1/2 onion
Mushrooms
Garlic
Black pepper
Basil
Oregano

Preheat oven to 375. Dice the onions garlic and mushrooms and saute in a pan with olive oil or white wine. While that is cooking you can butterfly or tenderize the flank steak with a meat tenderizer. I tenderize it until it is really thin. Then score the meat. When the onions and everything are almost ready drain the can of diced tomatoes and throw them and the spinach in the pan. Season all of this with the basil, oregano, pepper and whatever else you want.

After all that cover the flank steak with the stuffing and roll up. I used tooth pick to hold together but it would be easier with the baking string. After its rolled up brown the steak in the panthat you just used. Let it bake in the oven until its ready, around 20 minutes. Depends on how thin you made the steak.

You can get the employee workign the meat are to butterfly the meat if you dont want to. I think it is better to tenderize it rather than just butterfly. Takes a little more time but really helps. Season however you want with whatever you want. This is the way I did it and turned out really good.

To make it "paleo-ish" top it with some parmesian cheese or just put in with the stuffing.