In a small bowl, combine garlic powder, smoked paprika, salt, black pepper, chili flakes, and Worcestershire sauce to create a marinade.

Rub the flank steak with 1 tablespoon of olive oil, coat thoroughly, then sprinkle the seasoning mixture over the steak.

Allow the steak to marinate for at least 10 minutes at room temperature.

Heat a skillet over medium-high heat, add 1 tablespoon of olive oil, then sauté the sliced onions and green bell peppers for about 7-8 minutes.

Add minced garlic in the last 1-2 minutes, then remove from heat and set aside.

Cook the marinated steak in the same skillet for 3-4 minutes per side or until desired doneness.

Let the steak rest for 5 minutes before slicing it against the grain.

Mix mayonnaise and Dijon mustard together, spread it on both sides of the sandwich rolls, then layer with sliced steak, sautéed veggies, and cheese.

Optionally, broil the assembled sandwiches for 1-2 minutes for melted cheese.

Top with fresh arugula or lettuce and serve immediately.