Remove and reserve the prawn heads and tails, then devein the prawns. Transfer the prawn meat into a bowl and set aside. Place the prawn heads, tails and 20g of the oil into the mixing bowl and cook for 5 minutes/Varoma/speed 1.
Add the water and cook for 20 minutes/100C/speed 1. Place a fine-mesh sieve over a large jug and strain the prawn stock into it. Discard the contents of the sieve. Clean and dry the mixing bowl.
Place the courgette pieces into the mixing bowl and chop for 3 seconds/speed 4. Transfer into a separate bowl and set aside.
Place the onion, garlic and remaining 30g of oil into the mixing bowl and chop for 3 seconds/speed 5.
Scrape down the sides of the mixing bowl with the spatula, then cook for 3 minutes/ 100C/speed 1.
Add the rice and cook for 2 minutes/100C/reverse/speed 1.5, without the measuring cup.
Add the wine and cook for 2 minutes/100C/reverse/speed 1.5, without the measuring cup. Scrape the bottom of the mixing bowl well with the spatula to loosen the rice.
Add the salt, reserved courgette and 750g of the reserved prawn stock, and cook for 13 minutes/100C/reverse/speed 1.5, placing the simmering basket instead of the measuring cup onto the mixing bowl lid.
Add the butter, lemon juice and reserved prawn meat. Mix with the aid of the spatula, then cook for 2 minutes/100C/reverse/speed 1.5, placing the simmering basket instead of the measuring cup onto the mixing bowl lid. Transfer the risotto into a thermal serving bowl or other large bowl and cover to keep warm for 2 minutes before serving. Season, to taste.