Prepare the Tuna Salad : In a medium bowl, mix drained tuna with mayonnaise, Dijon mustard, lemon juice, chopped onion, celery, and shredded carrot. Season with salt and pepper to taste.
Prepare the Tortillas : Lay out tortillas flat on a clean surface. Place a layer of lettuce or spinach in the center of each tortilla.
Assemble the Wraps : Spoon tuna salad onto the greens. Add cucumber, bell pepper, shredded carrots, and optional toppings like avocado or sprouts.
Roll the Wraps : Fold the sides of the tortilla over the filling and roll tightly from bottom to top. Secure with a toothpick if needed.
Serve : Slice each wrap in half diagonally for easier handling. Serve immediately with a side of fresh fruit or chips.