In small bowl, whisk soy sauce, lime juice and ginger. Makes about ¾ cup.
Reserve ¼ cup soy sauce mixture. Place tuna in large zip-top plastic bag; pour remaining ½ cup soy sauce mixture into bag. Seal bag, pressing out excess air; gently massage tuna in bag to coat. Refrigerate tuna at least 1 or up to 4 hours.
Remove tuna from marinade; discard marinade. In large nonstick skillet, heat oil over medium-high heat. Add tuna; cook 5 minutes or until internal temperature reaches 145° or to desired doneness, turning once. Slice tuna ¼" thick.
Prepare rice as label directs. Makes about 2 cups.
Divide rice into 4 bowls; top with avocado, pepper, mango, cucumber and tuna. Serve drizzled with reserved ¼ cup soy sauce mixture.