Rinse uncooked quinoa and place in saucepan with 1 - 1 1/2 cups water (ratio of water to quinoa should be 2:1). Bring to a boil, reduce heat & cover. Cook until all liquid is absorbed, about 20 minutes. Let it cool - this can be done a day ahead if desired. Combine juices, agave & oil - wisk together & set aside. In separate bowl, chop & combine the cucumber, mango & berries.
In shallow bowl, marinate the tuna in olive oil & sea salt and coat on one side with sesame seeds. Heat up grill or grill pan. When pan is hot, sear tuna on each side, about 3 minutes each.
Combine quinoa, fruit mixture & liquid. Mix well, top with the tuna & serve!