Prepare the marinade: In a small bowl, melt the butter. Add lime juice, smoked paprika, garlic powder, chili flakes (if using), black pepper, and salt. Stir until well combined.

Prep the slow cooker: Place the halved onion and garlic head (cut side up) at the bottom of the slow cooker. Lay the rosemary sprigs on top.

Prepare the turkey breast: Pat the turkey breast dry with paper towels. Trim any excess fat or skin. Using your hands or a brush, generously coat the turkey with the marinade, ensuring every surface is well-covered.

Assemble and start cooking: Place the marinated turkey breast on top of the onion, garlic, and rosemary in the slow cooker. Pour the chicken broth around the base of the turkey, ensuring the liquid doesn’t wash off the marinade. Cover with the lid.

Cook low and slow: Set the slow cooker to low and cook for 6-8 hours, or until the turkey reaches an internal temperature of 165°F (74°C) at the thickest part.

Finish and serve: Once cooked, carefully remove the turkey breast from the slow cooker and set it aside on a cutting board to rest for 10-15 minutes. Meanwhile, remove the aromatic vegetables (onion and garlic) from the slow cooker and discard them. Shred the turkey breast gently using two forks, then return the shredded meat to the slow cooker. Mix it with the juices at the bottom to ensure every bite is moist. Serve warm and enjoy!