Select a ripe pineapple and slice off the top and bottom.
Remove the skin and core, then chop the pineapple into small cubes.
Finely chop the red onion and jalapeño.
In a mixing bowl, combine the diced pineapple, onion, jalapeño, and red bell pepper.
Add freshly chopped cilantro and lime juice.
Season with salt to taste.
Fold in diced avocado if using.
Serve immediately or chill for 30 minutes to enhance flavors.