Preheat your grill to very hot.
Brush the tuna with olive oil and season with salt and pepper.
Grill each side for only 2 to 2 1/2 minutes. The center should be raw, like sushi, or the tuna will be tough and dry. Allow to rest for 5 to 10 minutes and serve.
While tuna is resting, grill the pineapple: Place the pineapple slices on the hot grill. Brush with your favorite Teriyaki Sauce.
When the pineapple has grill marks on the underside, flip and grill the other side.