Pineapple Salsa:
Toss all ingredients together in a large bowl. Serve immediately or cover and chill until ready to use.
Tuna Steaks:
In a large bowl, mix together the orange juice, soy sauce, sesame oil, lemon juice, garlic, thyme, and pepper. Set aside 1/2 the marinade. Place the tuna steaks in the marinade and turn to coat. Cover, and refrigerate for at least 30 minutes.
Preheat grill for high heat.
Oil grill grate. Cook the tuna steaks for 4 minutes, then turn and baste with the marinade. Cook for an additional 4 minutes, or to desired doneness. Baste the fish continually. Ensuring that the fish remains moist. Remove from the grill and allow to sit for 5 minutes. Serve with salsa.