Place stock and ½ cup water in a saucepan. Bring to a simmer over medium heat.
Heat butter and 2 tbsp oil in a large heavy based saucepan, cook onion, stirring, until tender. Add rice, stirring to coat. Add wine and 1 cup of warm stock, bring to the boil. Reduce to a simmer, stirring occasionally, until liquid is almost absorbed.
Add 1 cup of warm stock to the rice, stirring occasionally, until absorbed. Repeat until all the stock has been used, cooking for 20-25 mins or until rice is just tender.
Heat a large heavy-based frying pan over medium heat. Season barramundi all over with sea salt and freshly ground pepper. Drizzle with 2 tbsp olive oil and rub into the skin and flesh.
Place barramundi, skin-side down in the heated pan and cook for 7 mins, turn and cook for another 5 mins. Transfer to a plate to rest.
Meanwhile place peas in a saucepan of salted water and bring to a boil, once boiling add asparagus and cook for 2 mins. Refresh under cold water and drain.
Stir peas, asparagus, lemon zest and juice, parmesan and mint through the risotto. Season.
Divide risotto between 4 plates, top with barramundi and microgreens and serve.