In a shallow bowl, combine lime juice and sugar.
Add pineapple and toss to coat thoroughly.
Let marinate for 30 minutes.
Remove pineapple and set aside.
Transfer marinade to a saucepan over medium heat.
Add vinegar and simmer, stirring often until reduced by half.
Remove from heat and cool to room temperature.
Preheat grill to medium high.
Wipe grill with an oiled towel and place pineapple on grill at an angle.
Cook for 6-8 minutes, turning frequently until outside of pineapple is lightly golden and caramelized.
Remove from grill, let cool and dice into 1/4-inch pieces.
In a bowl, combine pineapple with reduced vinegar mixture.
Gently toss in onion, jalapeno, cilantro, olive oil, salt, pepper, and avocado.
Taste and adjust seasoning as necessary.