Lightly spray a non-stick saucepan with cooking oil spray, and heat over moderate heat. Cook onion and curry powder for 1 minute over moderate heat. Add rice and cook 2 minutes. Add stock and bring to the boil. Reduce heat and simmer, covered for 8 minutes.

Add prawns and simmer, covered for further 4 minutes. Stir lemon juice, parsley & lemon zest (optional) through rice and stand, covered 5 minutes.