Bring water to a boil with 1 tbsp salt per liter. Add the whole tofu block and boil for 5 minutes. This firms it up and improves flavor.
Let it cool down a bit so you can handle it. Meanwhile, finely chop your onion, spring onion and lemongrass.
Mash the tofu in a bowl, then mix in all the aromatics, seasonings, and sauces.
Add oat flour one tablespoon at a time until you can easily form balls that hold their shape.
Pan-fry the balls until golden on the outside.
Transfer to an airfryer and crisp up at 200°C for 10 minutes until evenly golden.
Serve hot with a dip or in your bún chả or bánh mì.
