In a large bowl, combine ground turkey, parsley, Worcestershire sauce, onion salt, and pepper.

Shape the turkey mixture into 4 patties.

Set the patties aside.

Melt butter in a large skillet over medium heat.

Add sliced fresh mushrooms to the skillet.

Cook and stir for 2-3 minutes, or until the mushrooms are tender.

Remove the mushrooms from the skillet and cover to keep warm.

Add the turkey patties to the skillet.

Cook on medium heat for 12-14 minutes, or until the patties are cooked through, turning occasionally.

Place a patty on the bottom half of a hamburger bun.

Top the patty with the sautéed mushrooms.

Add the top half of the bun to complete the burger.

Lightly butter and toast the hamburger buns before assembling the burgers.