Heat a griddle over medium-high heat long enough to get it good and hot. With a metal spatula, spread the oil around on the hot surface. Scatter the onions and bell peppers on the griddle. Sprinkle with Creole seasoning.
Cook the onions and bell peppers until they're soft and lightly browned here and there. Move them off to the cool side of the griddle.
Spread the slices of beef out over the hot part of the griddle. Using a second metal spatula, hold the beef down while using the other spatula to scrape across the beef, causing it to shred away. Cook until all the pink is gone from the meat.
Lower the heat to almost nothing. Bring the onions and peppers back to the hot part of the griddle, spread it out, and deposit the beef on top of it. Cover the whole pile with the slices of provolone cheese. Leave it there until it softens, but not until it melts.
While waiting for that, slice the bread from end to end and put it into the oven.
Spread a very little bit of Creole mustard over one side of the bread. Moved the cheese, meat, peppers and onions onto the bread, and cover with the other half. Serve immediately.
