Spray slow cooker with cooking spray. Spread the sliced onions all over the bottom of the slow cooker.
Sprinkle salt and pepper all over the pork roast. Place it inside the slow cooker, on top of the onions.
In a large bowl, combine broth, vinegar, honey, Worcestershire sauce, and garlic. Stir until incorporated. Pour over the roast.
Cook on low for between 6 and 8 hours, depending on the size.
When cooked, remove roast. Place on a serving plate.
Either turn slow cooker up to high or pour juices into a saucepan on the stove over medium high heat.
Combine flour and water in a cup. Stir until incorporated. Pour flour mixture into slow cooker or saucepan and whisk.
When mixture starts to thicken as liquid simmers, between 10-20 minutes covered in the slow cooker, or a few on the stove.
Remove from heat and serve with your roast! Enjoy every bite!