Preheat grill to medium heat.
Remove exterior pineapple skin and place pineapple on grill briefly until char-marked on all sides.
Cool completely, then separate 1/4 of pineapple for salsa; remove core then cut into 1/4-inch-thick slices.
Place red bell pepper on the grill until skin is blistered, then peel, seed, and chop into 1/4-inch diced pieces.
Peel onion, slice into 1/4-inch thick slices, and grill until browned.
Cool completely, then dice into 1/4-inch chunks.
Combine all ingredients in a medium bowl and mix until well-combined.
Chill until serving.