Start by mixing salt, pepper, paprika, chili powder, garlic powder, onion powder, thyme, marjoram, and basil in a small bowl. Place the thinly sliced beef sirloin in a large mixing bowl, then sprinkle the seasoning mixture over it. Toss everything together until the beef is evenly coated.

Heat half of the vegetable oil in a skillet over medium-high heat. Once the oil is hot, add the seasoned beef. Cook the beef, stirring occasionally, until it’s browned and cooked through. Remove it from the skillet and set it aside on a plate.

Add the remaining vegetable oil to the skillet. Toss in the onions and green bell peppers, stirring frequently. Cook the vegetables until they’re tender and caramelized, usually around 8-10 minutes. This step gives the sandwich its signature sweetness and flavor.

Preheat your oven's broiler. Lay the split hoagie rolls on a baking sheet. Divide the cooked beef evenly between the rolls. Top the meat with the caramelized onions and bell peppers, then layer slices of Swiss cheese on top.

Place the loaded hoagie rolls under the broiler for 1-2 minutes, or until the cheese is fully melted and bubbly. Keep an eye on it to avoid burning.

Once the cheese has melted, place the top halves of the rolls on the sandwiches. Serve immediately and enjoy the warm, cheesy goodness of your homemade Philly cheesesteak sandwiches!