In a small bowl, mash the avocado using a fork, mix it with the lemon juice and season it with salt. Set it aside.
For the turkey patties, combine all the ingredients in a bowl, except the olive oil. Separate the mixture into two equal parts and form two patties. Set it aside.
In another bowl, mix all the ingredients of the cabbage salad and season them well. Set it aside.
Heat the olive oil and brown the patties (5 minutes per side) on a non-stick skillet over medium heat.
In the same pan, brown the inside of the buns.
Garnish the base of each bread with mashed avocado, a turkey patty, coleslaw and watercress, then close it with the remaining bread.