For the sauce: Melt the butter in saucepan over medium-low heat. Add the flour and stir until blended. Slowly whisk in the milk until the sauce thickens, stirring constantly, about 5 minutes. Stir in the cheese until melted.
For the philly: Heat the oil in a pan over medium-high heat. Add the onions and green peppers, tossing around to flavor the oil, until starting to change color, 10 to 12 minutes. Add the steak and start chopping using a spatula, moving it around the skillet until there's a sprinkling of both browned and red meat. Add the seasoning salt, some sea salt, black pepper, olive oil, vinegar and oregano. Really dig the spatula into the meat, moving it around until it's all cooked evenly, about 2 minutes, depending on desired doneness.
Lay the meat onto the rolls and top with the smoked Gruyere cheese sauce. Serve with salty potato chips.