Preheat the oven to 375 degrees F.
On a parchment-lined sheet pan, drizzle olive oil, starting in the center and covering an area approximately 8 inches by 10 inches on the parchment.
Add sliced onions, sliced tomatoes, sliced mushrooms, and chopped parsley—season with salt and pepper.
Add the cooked shredded chicken on top of the seasoned vegetables.
If using Alfredo sauce, drizzle it over the chicken.
Cover the chicken and vegetables with the in-tack sheet of crescent roll dough. Lightly press the edges of the dough into the parchment paper.
Brush the crescent roll dough with melted butter and bake for 15-20 minutes, or until the dough is golden brown and the center of the dough is cooked through. Use a toothpick to test and ensure the center of the dough is cooked.
Let the sheet pan rest for 5 minutes.
Use a cutting board or a serving platter that is large enough to cover the sheet pan. Carefully cover the sheet pan with the board or platter. If the pan is too hot, wear oven mitts and flip the sheet pan onto the board or platter so that the parchment paper is on top.
Slowly peel the parchment paper off the top and scrape any bits stuck to it, then add them back to the top of the chicken sheet pan.
Slice and serve.