In a mixing bowl, combine drained tuna, mayonnaise, chopped celery, dijon mustard, and chopped red onion. Mix until well combined.

Heat a skillet over medium heat.

Lay a tortilla flat and place a portion of the tuna mixture in the center. Sprinkle with shredded cheese.

Fold the sides of the tortilla over the filling, then roll it up tightly from the bottom to create a wrap.

Place the wrap seam-side down in the skillet. Cook for 2-3 minutes on each side until golden brown and the cheese is melted.

Repeat with remaining tortillas and filling.