Grab a large skillet and set it over medium heat. Brown the ground beef along with your diced onion. Once the beef is no longer pink, drain off any excess grease.
Sprinkle the taco seasoning over the beef and onion. Stir it in really well and let it cook for just another minute or two.
Take the skillet off the heat. Stir in your shredded cheddar cheese, the nacho cheese sauce, your drained diced tomatoes, and the optional sliced jalapeños. Mix everything together until well combined.
Lay one egg roll wrapper down on a clean surface so a corner is pointing towards you, like a diamond. Place about 2-3 tablespoons of the beef and cheese mixture just below the center of the wrapper.
Fold the bottom corner snugly up over the filling. Then, fold in the left and right corners towards the center.
Starting from the folded bottom, roll the wrapper tightly upwards towards the final corner at the top. Just before you reach the end, dip a finger in a little water and moisten that top corner. Finish rolling to seal it up.
Repeat this process with the remaining filling and wrappers until you have a pile of ready-to-fry egg rolls.
Pour about 2-3 inches of your chosen oil into a large pot or deep fryer. Heat the oil to 350°F (175°C). (If no thermometer, test oil with a tiny piece of wrapper - it should sizzle and bubble immediately but not burn instantly).
Carefully place a few egg rolls into the hot oil. Do not overcrowd the pan.
Fry for about 3-5 minutes, turning them occasionally, until golden brown and crispy on all sides.
Carefully remove them from the oil using a slotted spoon or spider and place them on a wire rack set over paper towels to drain excess oil.
Serve them hot with optional dipping sauces like sour cream, salsa, guacamole, or ranch dressing.