Heat a grill pan over medium-high heat until hot. Place the pineapple slices in a single layer on the grill and cook, undisturbed, until grill marks appear, about 3 minutes per side. Transfer the pineapple to a plate and let cool.
Lightly brush the tops and bottoms of the scallops with the oil and season with salt and pepper. Working in batches if necessary, grill the scallops until marks appear, 3 to 4 minutes per side.
Meanwhile, combine the bell pepper, shallot, jalapeno, garlic and chopped cilantro in a medium bowl. Chop the cooled pineapple, add to the bowl and season with salt and pepper. Just before serving, stir in the lime juice.
Divide the salsa among 4 plates, top with 3 scallops each and garnish with the cilantro leaves.
