Put rice and 500 ml boiling water in a large microwave-safe bowl.
Cover with plastic film and microwave on high for 7 minutes, or until all the liquid is absorbed. Allow to cool a little.
In the meantime, put tuna into another large bowl and mash with a fork to break down the chunks.
Add corn, peas, eggs, spring onion, mayonnaise, 40 g rice crumbs and season with salt and pepper. Combine.
Add tuna mixture to cooked rice and stir to combine.
Using very clean hands, shape dessert spoonfuls of the mixture into round discs.
Put remaining 50 g rice crumbs into a bowl and roll the discs in the crumbs, gently shaking off the excess.
Put onto a clean plate. Repeat with the remainder of the mixture.
Cover plate with plastic film and refrigerate for 30 minutes.
In a large fry pan, heat oil on a medium-high temperature. Fry the cakes in batches, approximately 10 minutes on each side, or until golden brown and cooked through.
Drain on a wire rack and serve immediately, with green salad and mashed potato.