I’ve made the Watermelon Tuna multiple times in the past few weeks, but every time I do, it still blows my mind. These oven roasted, soy-marinated watermelons achieve a total change in texture and taste, making them a good substitute for tuna. Get seated, It’s time for some plant-based omakase!

Let’s get straight into what kind of magic I’ve done to the watermelon to transform them into tuna. The process involves three main steps: 1) Marinate. 2) Roast. 3) Marinate.
Okay, that’s only three words. But if you really took your time, you can do this for a few days, especially the marinating part (granted, the more you marinate, the more tender & flavorful your watermelon will become!). The initial marinade consists of soy sauce, sesame oil, mirin, and seaweed flakes — it’s meant to help you infuse all those familiar umami and briny flavors into the watermelon.
Roasting Watermelon
Yep, you read that right. We’re roasting the watermelon to give it that slightly squishy yet firm tuna texture. The roast is a very slow one — the low temperature will slowly tenderize the watermelon without charring or caramelizing it, so as to retain that raw look.


The final marinade is a brief but important one. After a couple of trials, I realized that when you place the hot watermelon (after roasting) back into the cold marinade, you not only allow the watermelon to cool down quicker, but allow the watermelon to re-absorb all that umami flavor from the marinade.
Great recipe, not vegan though. Here in the US, most white white sugar is not vegan unlike Canada and most of the rest of the world.
Hello Angelo!
Thanks for pointing that out! However, I’m based in Taipei, Taiwan and i’m using a local brand of sugar. I’ve checked that the sugar I use is indeed vegan — if you’re based in the US, you just need to make sure you’re buying organic sugar (that is not filtered through bone char).
This looks incredible! What brands would you recommend? I’m especially curious about the seaweed flakes, since I’ve never used them before.
Hi Eric,
I’m currently in the process of adding the brands of ingredients that I use to the website! For the seaweed flakes, I actually just chopped up some nori sheets. You should be able to find dried seaweed flakes in most Asian groceries though.
Looks amazing Jorge!! I can’t wait to try this 🙂 I’ve never really liked raw fish before going vegan, but my bf and dad do so I will make this for them. Will update once I do! Thank you so much again, your posts always look so delicious!!!
Hi Anna, thank you for this heartwarming message :’) Sounds great! Let me know when you’ve made it by tagging me on instagram, I’d love to see it!
Hey George! After roasting, how long can the softened watermelon keep in the fridge before you have to eat them? Kinda want to make them in large batches/meal prep style since the roasting time is a bit long.
Hi em, I would say it could keep for a couple of days in the marinade! I’ve left it for around 3 days in the marinade but I think it could last a tad bit longer.
For all those wondering: I made this last night and tried it just a moment ago! I ate it as a “sashimi” paired with some real tuna sashimi for some comparison. My notes: – I made 3 separate size comparisons (Nigiri “slices”, “sashimi block”, and cubes like in the recipe). – the marinade is not simply scalable for the weight of watermelon (I made ~5x the amount and had a lot of leftover marinade I saved for future cooks) – the marinating and cooking makes it quite salty for my tastes, so I actually decided to rinse& quick-soak the final… Read more »
[…] Prepare the Sushi Rice. Take some freshly steamed rice and place it into a bowl. Add the rice vinegar and sugar and mix well — do this while the rice is still hot so the sugar will melt. To shape the rice, dampen your hands with water and shape the rice into ovals. I also prepare sushi rice in a similar fashion in my Watermelon Sushi Recipe. […]