Place the flank steak on a cutting board with the short end closest to you. Starting from one of the long sides, cut through the meat horizontally to within 1/2 inch of the opposite edge. (You can also ask your butcher to butterfly the flank steak for you instead of cutting it yourself.)
Mix the soy sauce, olive oil, and steak seasoning together in a gallon-sized resealable plastic bag. Marinate flank steak in the refrigerator 4 hours to overnight.
Preheat oven to 350 degrees F. Grease a 9×13 baking dish.
Lay out the flank steak flat in front of you with the grain of the meat running from left to right. Layer the provolone across the steak, leaving a 1-inch border. Arrange spinach, red pepper, and mushrooms across the cheese covered steak in stripes running in the same direction as the grain of the meat. Roll the flank steak up and away from you, so that when the roll is cut into the pinwheel shape, each of the filling ingredients can be seen. Roll firmly, but be careful not to squeeze the fillings out the ends. Once rolled, tie every 2 inches with kitchen twine.
Place in a foil lined baking dish, and bake in preheated oven for one hour, or until the internal temperature reaches 145 degrees F. Remove from the oven and let rest for 5 to 10 minutes before cutting into 1 inch slices. Be sure to remove the twine before serving!
Serve with garlic mashed potatoes, spinach salad and beverage.