Preheat oven to 350 degrees F.
Remove the duck from refrigerator. Drain excess marinade. In a large oven-proof skillet over high heat, sear the duck breasts on both sides until brown. Transfer to the oven and roast until done. Let cool. Remove the skin and dice the meat.
Combine the mango, pepper, lime, and cilantro and refrigerate.
Gently warm the tortillas. Spread diced duck breast evenly on each half of each tortilla. Top each with cheese. Fold tortilla. Lightly oil a grill pan and grill until light brown on both sides and cheese is melted. Slice each tortilla into 5 wedges and garnish with mango salsa and sour cream.