Heat olive oil in a large skillet over medium heat. Add the diced onions and green pepper, cooking until softened, about 3-4 minutes. Toss in the mushrooms and minced garlic, then cook for another minute. This step releases the natural sweetness and aromas of the veggies, making your meatloaf irresistibly flavorful. Set the mixture aside to cool slightly.

Combine the ground beef, ketchup, Worcestershire sauce, eggs, salt, pepper, panko breadcrumbs, and the cooled veggie mix in a large bowl. To get the best texture, mix gently with your hands until just combined. Overworking the mixture can make the meatloaf dense, so handle it with care.

Line a baking sheet with foil or grease your loaf pan. Transfer the meat mixture, shaping it into a neat loaf. You can make two smaller loaves if you prefer quicker cooking or want to save one for later. A freeform loaf allows for browning on all sides, creating extra flavor.

Preheat your oven to 375°F. Bake the meatloaf for about 50-60 minutes, depending on its size. Check to ensure it’s cooked through (internal temperature should reach 160°F). For an extra touch of magic, broil the meatloaf for 3-5 minutes, which gives the edges a crave-worthy caramelized finish.

Top the hot meatloaf with slices of provolone cheese. Pop it back into the oven just long enough for the cheese to melt into gooey, golden perfection. This final step nails that Philly cheesesteak essence, making every bite irresistible.