Coat a 6 qt. Slow cooker with nonstick cooking spray. Place roast into slow cooker; season with onion salt and black pepper.
Drain peaches, reserving the syrup. In a bowl, whisk syrup, chilisauce, brown sugar, vinegar and pumpkin pie spice. Pour over meat; scatter peach slices over the roast. Cook 3 hours on high or 6 hours on low.
Remove meat and allow to rest for 10 minutes. Spoon out peach slices and reserve. Place liquid in a small saucepan and bring to a boil over medium-high heat. Stir in cornstarch mixture and cook, stirring for about 30 seconds until the sauce thickens.
To serve, slice meat and scatter reserved peach slices over the top. Serve with sauce on the side and egg noodles if desired.