Spread out your puff pastry dough on a sheet of parchment paper or wax paper (this will help in the rolling process). On the lower 1/3 of your dough, place the pounded chicken, side by side leaving room and the left and right side to seal the log later. Next place the sliced cheese on top of the chicken, just one layer, until the entire surface is covered. Place spinach in a horizontal line across the chicken, then top that with a line of the mushroom-onion mixture. Next, using the parchment paper, fold the dough over so that the chickens roll in half. Continue rolling the dough until it forms a log. Pinch the dough at the end to create a seam. Then fold and pinch the ends to seal. Place the roll in a greased loaf pan or roasting pan and place in a 350'F (177'C) oven. Cook until internal temperature reaches 160'F (71'C).