In a large skillet, heat a tablespoon of olive oil over medium heat. Add the chopped onion and bell pepper, sautéing for 3-4 minutes until the vegetables are softened.
Add the minced garlic to the skillet and cook for an additional 1-2 minutes until fragrant.
Increase the heat to medium-high, and add the ground chicken. Cook until the chicken is browned and cooked through, breaking it apart with a spoon, about 5-6 minutes.
In a mixing bowl, combine the ketchup, Worcestershire sauce, apple cider vinegar, brown sugar, smoked paprika, cumin, salt, and pepper. Mix well.
Pour the sauce mixture over the chicken in the skillet, stirring to combine. Let it simmer for about 5 minutes, until the sauce thickens slightly and everything is heated through.
Toast the hamburger buns if desired. Then, spoon the mixture onto the bottom half of each bun, and top with fresh cilantro if using.
Serve immediately with the top half of the bun alongside, allowing everyone to assemble their Sloppy Joes as they wish.
Notes
Consider serving with sweet potato fries or a crisp salad.