In medium saucepan, combine rhubarb, tomato purée, apple cider vinegar, coconut sugar, honey, Worcestershire sauce, smoked paprika, garlic powder, onion powder, and salt. Cook over medium heat for 15 to 20 minutes, stirring occasionally, until rhubarb breaks down and mixture thickens. Let cool slightly, then blend until smooth. Set aside.
In large skillet over medium heat, combine shredded chicken and 1/2 cup of Rhubarb BBQ sauce. Stir to coat evenly and heat through, about 3 to 4 minutes.
In large bowl, toss together shredded cabbage, grated carrot, apple cider vinegar, honey, olive oil, salt, and pepper. Let sit for 10 minutes to allow flavors to meld.
Toast slider buns lightly for extra texture. Place generous scoop of pulled chicken on bottom half of each bun. Top with spoonful of slaw and the top of bun.
Serve warm, with extra BBQ sauce on the side for dipping.