Before we arrived in the Marquesas, people made a point of telling us how difficult it was to find vegetables there. We heard that if we wanted tomatoes, we would need to get up at 4am to get them at the market. Devine & I are early risers, but we lacked the will to take the dinghy to shore in the dark. It's just as well, because others we met who had tried, came back empty handed. In the marquesas, most vegetables are brought in by supply ships; you can never be certain of what you're going to get. Potatoes, cucumber, cabbage and eggplant we had plenty of, but vegetables like tomatoes, pumpkins, bok choy and salad greens, were like rare pokemon.
We'd only ever made bruschetta topping with tomatoes, never thought of changing it for anything else - why would we? Tomatoes were not in short supply then. While we were in Mexico, friends of ours made the most amazing tomato-less salsa; they used watermelon, and i remembered this when we craved bruschetta in Nuku Hiva. What looks sort of like tomatoes? Papaya! Not that they look that much alike; they have a reddish tint, comparable texture too. Papaya is something Nuku Hiva has plenty of; and as it turns out, since we started to make bruschetta with it, we prefer it over tomatoes now. Papaya is more firm and sweet, and pairs even better with balsamic vinegar. I imagine it would taste great with mangoes too, it's something i may try when i get a craving again.
If something isn't available, or is too expensive where you are (hunting for raspberries in japan comes to mind), swap it out for something else. Not every will work, but it's fun to try isn't it?