In a large bowl, whisk together the pineapple juice, brown sugar, ketchup, soy sauce, chicken broth, ginger, and garlic. Reserve one cup of the marinade for later use. Add the chicken to the main bowl and coat it thoroughly in the marinade. Cover and refrigerate for at least 30 minutes.
In another large bowl, combine the diced pineapple, mango, avocado, chopped cilantro, and lime juice. Gently toss everything together until well combined. Cover your salsa and set it aside.
Heat a grill pan over medium heat and lightly brush it with oil. Drain the chicken from its marinade and place it on the grill pan. Grill covered for about 6–8 minutes per side until no longer pink inside. Dice your chicken into small pieces.
Take your mini corn tortillas and divide the diced chicken evenly among them. Top each taco generously with your fresh salsa. Serve immediately.