In a large bowl, whisk together the pineapple juice, brown sugar, ketchup, soy sauce, chicken broth, ginger, and garlic. Reserve 1 cup of the marinade in a separate bowl and set aside. Add the chicken to the main bowl and coat thoroughly. Cover and refrigerate for 30 minutes.
In a large bowl, add the pineapple, mango, avocado, cilantro, and lime juice. Toss gently to combine, then sprinkle with sea salt, cover, and set aside.
Heat a grill pan over medium heat and gently brush with oil or cooking spray. Drain the chicken and discard the marinade, then grill, covered, for 6-8 minutes per side, or until no longer pink and a meat thermometer inserted into the thickest portion reads 165 degrees. Baste occasionally with reserved marinade, then dice the chicken into small pieces.
Divide the chicken and salsa between the tortillas and serve immediately.
Divide the reserved marinade before basting to avoid contamination, so you can use half to drizzle over finished tacos, if desired.