Spray slow cooker with cooking spray. Place onions on the bottom of the slow cooker and the pork roast on top. In a bowl combine honey, soy sauce, red wine vinegar, mustard, salt, garlic, and pepper. Pour over the top of the pork roast and cook on low for 5-7 hours, depending on the size of your roast. When roast is cooked remove it from your slow cooker and allow it to rest on a plate. Turn slow cooker up to high or pour juices into a saucepan on medium high heat on the stove. Combine flour and water and add to slow cooker or saucepan. Boil until sauce starts to thicken. Serve with the pork roast. Enjoy!