Heat a large skillet over medium-high heat and add a tablespoon of oil. Add the diced onion and sauté until translucent, about 3-4 minutes.

Add the ground beef to the skillet, breaking apart with a spatula as it cooks. Stir frequently for about 5-7 minutes until browned.

Sprinkle taco seasoning over the beef, mixing well to coat evenly. Reduce heat to low and layer the shredded cheeses over the beef, covering with lid for 1-2 minutes until melted.

Slice the hoagie rolls in half. Heat another skillet and if desired spread mayonnaise on cut sides, then toast rolls for 2-3 minutes until golden brown.

Spoon the cheesy beef mixture on the bottom half of each roll. Top with diced tomatoes, cilantro, and sliced jalapeños.

Place the top half of the roll over the filling, pressing gently and slice each sandwich in half for easy handling.