Preheat oven to 400 degrees. Bring pineapple juice, brown sugar, and mustard to a boil in a small saucepan, stirring to dissolve sugar. Boil until glaze has thickened slightly, about 1 minute. Season with salt and pepper.
Mix pineapple, red pepper, cilantro, onion and chiles in a medium bowl. Season with salt and pepper.
Line baking sheet with foil. Place chicken on sheet and brush with glaze. Bake 15 minutes. Brush again with glaze, then broil until cooked through and golden, watching closely to avoid burning, about 5 minutes longer. Let rest 5 minutes. Spoon salsa over chicken and serve.