Mix all of the marinade ingredients together in a bowl and pour it into a large gallon-sized resealable plastic bag. Add the steak and turn to make sure it is completely covered by the marinade. Refrigerate for at least 2 hours and up to 12, turning the bag occasionally.
Melt the butter in a heavy bottomed saucepan over medium heat. Once melted add the flour and stir until it becomes a light blonde color. Slowly whisk in milk. Bring the milk up to a simmer while stirring. Once at a simmer, stir in the cheese, a handful at a time. Season with salt and pepper, to taste. Keep warm until ready to use.
Preheat the grill to medium-high heat.
Toss green onions in a bowl with olive oil, and salt and pepper, to taste.
Remove the steak from the marinade and let the excess drain off. Grill the steak for 5 to 7 minutes per side for medium-rare and about 8 to 10 minutes for medium. Remove the steak from the grill to a cutting board and allow it to rest for 10 minutes before slicing.
While the steak rests, put the green onions and baguettes on the grill. Cook the green onions until charred and soft, about 4 minutes, and toast the bread until golden.
To assemble, slice the steak, at a 45 degree angle, into very thin slices across the grain. Put some of the steak on the bottom of each roll, top with some grilled green onions, and smother with provolone cheese sauce. Cover with the top of the roll and serve.