Remove and discard net from pork roast. Place in crock of slow cooker. Arrange onion over the meat, and pour beans and enchilada sauce over the roast. Cover and cook on low for 8-10 hours. Flip roast over halfway through cooking if possible.
When ready to serve, remove cooked roast from crockpot to a large cutting board. Carefully pour remaining contents of slow cooker into a colander to drain off the liquid. Shred cooked meat with two forks, removing and discarding large pieces of fat as you work. Return shredded meat and drained beans and onions to cooking vessel or a serving bowl.
To assemble burrito bowls, place lettuce in the bottom of a large salad bowl. Place warm, cooked rice over the lettuce (optional), and place a generous helping of pork and beans over the rice. Pile on your desired toppings, and dig in!