Spray a large non-sticking frying pan with olive oil and set over medium-high heat. Cook chicken for 5 minutes until golden. Remove chicken from pan and cover to keep warm.
Spray the pan with a little more oil and return to medium heat. Gently fry onion and capsicum for 3 minutes until softened. Add tomatoes, rice, and Cajun seasoning. Cook for a further 2 minutes until the tomato is soft and the rice is heated through.
Add cooked chicken and rocket to the pan. Stir for 2 minutes, or until chicken is heated through and rocket is just wilted. Add a squeeze of lemon juice to seve.