How to Make It
Heat the oil in a large nonstick skillet. Season the shrimp with salt and pepper and cook over high heat for 1 minute. Add the onion and garlic and cook, stirring occasionally, until the shrimp are cooked through, about 2 more minutes. Stir in the orange juice, 2 tablespoons of the lime juice, the scallion and cilantro, transfer to a bowl and let cool.
Meanwhile, in a bowl, combine the remaining 2 tablespoons lime juice with the ginger, sesame oil, 1/2 teaspoon salt and 1/4 teaspoon pepper. Brush the pineapple with the mixture and let stand at room temperature for 30 minutes.
In a dry skillet, toast the sesame seeds over high heat, shaking the pan, until fragrant, about 2 minutes.
Light a grill or preheat the broiler. Grill or broil the pineapple for about 2 minutes per side, turning once, until lightly browned. Cut each quarter crosswise into 6 pieces and arrange the pieces on 6 plates. Set 2 shrimp on each plate, spoon on a little of the orange juice marinade and sprinkle with the sesame seeds.