Step 1

In a bowl, mix the drained tuna with mashed avocado, lemon juice, and chopped red onion.

Step 2

Season with salt and pepper to taste.

Step 3

Spread the mixture evenly on one slice of whole grain bread.

Step 4

Add optional toppings like lettuce leaves and tomato slices.

Step 5

Place the second slice of bread on top to complete the sandwich.

Step 6

Cut in half and serve immediately.