1. Sprinkle all sides of pork roast with salt and pepper. Cook roast in hot oil in a large skillet over medium-high heat 3 minutes on each side or until lightly browned. Transfer pork to a 6-qt. slow cooker, and add garlic, bay leaves, and onion. Whisk together brown sugar, soy sauce, and vinegar until sugar dissolves; pour mixture over pork. Cover and cook on LOW 8 hours.
2. Transfer pork to a serving platter, and cover with foil to keep warm. Pour cooking liquid through a fine wire-mesh strainer into a medium saucepan, discarding solids. Bring to a boil over medium-high heat; boil 8 minutes.
3. Spoon 1/4 cup cooking liquid into a small bowl, and whisk in flour and lemon juice until smooth. Return flour mixture to pan, and boil, whisking constantly, 1 to 2 minutes or until slightly thickened. Serve sauce over pork.