Creating a Tuna Salad Sandwich is simple when you follow these easy steps:

1. Drain Tuna: Open the tuna cans and drain the liquid thoroughly.
2. Combine Ingredients: In a mixing bowl, combine the drained tuna, mayonnaise, Dijon mustard, lemon juice, chopped celery, and chopped red onion.
3. Mix Well: Use a fork to mix the ingredients until well combined and creamy.
4. Season: Add salt and pepper to taste. Adjust seasoning as desired.
5. Chill (Optional): For enhanced flavor, cover the bowl and refrigerate the tuna salad for about 10 minutes. This step is optional but recommended for a cooler taste.
6. Prepare Bread: While the tuna salad chills, toast your bread to a golden brown, if desired.
7. Assemble Sandwich: On two slices of toasted bread, layer lettuce leaves and tomato slices. Generously spoon the tuna salad mixture on top.
8. Close the Sandwich: Top with the other slice of bread to complete the sandwich.
9. Serve: Cut the sandwich in half if you prefer and serve immediately.

Following these steps will help you create a scrumptious Tuna Salad Sandwich quickly and effortlessly!