Preheat a large skillet over medium-high heat and add a drizzle of oil. Add diced onions and sauté for about 3 minutes until translucent.

Add the ground beef to the skillet and cook for 4-5 minutes or until browned, stirring frequently.

Stir in the taco seasoning and cook for an additional 1-2 minutes.

Reduce heat to low, sprinkle cheeses over beef, cover the skillet, and let it sit for 1-2 minutes until cheese is melted.

Toast hoagie rolls cut-side down in another skillet over medium heat until golden brown.

Spread mayonnaise on each half of the rolls and layer cheesy beef mixture onto the bottom halves.

Top with diced tomatoes, cilantro, and sliced jalapeños if desired.

Close the sandwich with the top halves, press gently, and slice in half to serve.