If using whole bacon, fry on medium heat until fat has rendered. (You’ll be using it to sear the roast!) When done, remove bacon strips. (Eat them or dice and add to a side dish!) If you have the fat already on hand, you can use that instead.
Pat roast dry and season liberally with salt and pepper. Sear both sides on high heat until golden brown crust has formed, about 10 minutes on each side. When done, transfer to slow cooker. (The pan will smoke, so make sure you have lots of ventilation!)
Whisk together half of chicken stock (1 cup), Dijon, balsamic vinegar, maple syrup, smoked paprika, salt, and pepper in a medium bowl. Pour over roast in slow cooker.
Discard all but enough bacon fat to coat pan, add onions and cook on medium heat until slightly soft, about 5 minutes. Add remaining chicken stock and bring to a boil. Scrape up any bits stuck to the pan and transfer to slow cooker.
Cover and cook on low heat about 8 hours, until meat is tender and falls apart with a fork. Transfer roast to a serving platter and cover with foil.
Pour liquid into a large saucepan. Bring to a boil and cook until reduced to desired consistency. Pour over the top, or set aside to pour over individual servings.
Garnish with sprigs of fresh thyme and serve with whole roasted carrots, sauteed mushrooms and green beans!