Preheat the oven to 375°F (190°C).
Using a sharp knife, carefully butterfly each chicken breast by slicing horizontally to create a pocket, being careful not to cut all the way through.
Divide the haggis evenly among the chicken pockets, stuffing it inside each breast.
Wrap each stuffed chicken breast with two slices of prosciutto, overlapping slightly to fully cover the chicken and secure the filling.
Heat a large oven-safe skillet over medium-high heat and sear the wrapped chicken breasts for 2-3 minutes per side, until the prosciutto is crisp and golden.
Transfer the skillet to the preheated oven and bake for 15-20 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (74°C).
Remove from the oven and let rest for 5 minutes before serving.
Serve warm alongside roasted vegetables or a fresh green salad for a hearty, flavorful meal.