1. In a small bowl mash together the avocado, lemon juice and sour cream.
2. Spread the mayonnaise over one side of two slices of the wheat bread.
3. Spread the avocado mixture on one side of the other two slices of wheat bread.
4. Top the mayonnaise side of the bread with the shredded chicken.
5. Place the avocado spread slices of bread over the top.