New Recipe Idea - Cucumber Melon Tuna Tartar

I'm working on a new app idea for work. I was thinking about a regular tuna tartar (tuna, lime juice, salt and pepper, and olive oil) but adding cubes of cucumbers and cantaloupe and possible a little sugar to give it some sweetness. I want to serve it like sushi rolls. I'm looking for an idea for a sauce (maybe a key lime sauce?). Any feedback and ideas would be appreciated.