Heat a large skillet over medium-high heat and drizzle in a tablespoon of oil. Add the diced onion and sauté for about 3-4 minutes until they turn translucent.

Introduce the ground beef to the skillet, breaking it apart as it cooks. Brown for about 5-7 minutes, then mix in taco seasoning.

Reduce heat to low, layer cheeses over beef, cover, and cook for 2-3 minutes until cheese is melty.

Toast hoagie rolls cut-side down for 2-4 minutes until golden brown, then spread mayonnaise on both halves.

Spoon cheesy beef mixture onto the bottom half of each roll and top with diced tomatoes, cilantro, and jalapeños.

Close the sandwich with the top half of the roll, slice in half, and serve immediately.