Loosen the skin of the chicken breast and season underneath it with salt. Season the exterior of the chicken with more salt. Let the chicken rest for 30 minutes at room temperature. Line a broiler pan with foil and preheat the broiler.
Using a food processor, pulse the garlic and ginger until finely chopped. Add the brown sugar, soy sauce, broth, rice-wine vinegar and pineapple juice concentrate and process until well combined. Strain the marinade into a bowl, pressing with the back of a spoon to extract all the liquid. Discard the pulp.
Blot the excess salt and moisture from the chicken and place the halves skin side down on the broiler pan. Broil, turning the chicken with tongs every 5 minutes for the first 20 minutes, until the raw surfaces have cooked. Continue to cook, turning and basting with the marinade every 5 minutes, until well browned, 20 minutes longer; cover loosely with foil for the last 10 minutes. Cut into pieces and serve.