Heat a grill to medium-high. Very lightly oil the grates. Place the pineapple slices on the preheated grill and cook, turning once, until lightly charred on both sides. Remove from the heat and let cool to room temperature. Dice into medium sized chunks.
Split the avocados and scoop the flesh into a medium bowl. Mash with a fork or potato masher until mostly smooth. Stir in the onion, cilantro, lime juice, salt, and jalapeño and continue mashing until it has a fluffy whipped texture. Taste and adjust seasonings as necessary. Stir in the diced pineapple. Transfer to a serving bowl. Serve immediately with tortilla chips.