Preheat oven to 375 degrees F.
Prepare the dough: in a large jelly roll pan or cookie sheet, cover the bottom with parchment paper. Lay out the crescent rolls flat lengthwise, overlap the long sides to form a rectangle. Pinch together all the seams.
In a large bowl, combine chopped chicken, chopped broccoli, cream of chicken soup, cheese, salt, pepper, garlic powder & onion powder. Mix well.
Pour chicken mixture into the center of your dough rectangle, keeping it away from the sides and the top & bottom. Shape it into a log in the center.
Using a knife or scissors and starting at each side of the dough, cut "fringe" or horizontal strips all the way down the sides.
Braid the dough from the top, folding it over the top of the chicken mixture, alternating left and right, until you reach the bottom. (I lightly pinched the dough together after braiding to help contain the form better)
In a small bowl, beat together the egg yolk and about a teaspoon of water. Brush the top of the braid with the egg mixture. Sprinkle thyme, rosemary and additional cheese over the top if desired.
Bake for 28-30 minutes or until the braid is golden brown all over. Slice and serve.