Step 1 Place flour and paprika in a large zip-lock bag. Add chicken to bag and shake to lightly coat.
Step 2 Heat olive oil in a large, deep heavy-based frying pan set over medium–high heat. Add chicken and cook, turning occasionally, for 4–5 minutes, or until sealed and golden. Transfer cooked chicken to a plate; set aside.
Step 3 Spray same frying pan with olive oil again. Add sliced leeks and cook, stirring occasionally, for 3–4 minutes, or until soft. Add celery and garlic; cook, stirring occasionally, for 2 minutes.
Step 4 Add reserved chicken to frying pan with potatoes, lemon juice and chicken stock; season with cracked black pepper. Reduce heat to medium low. Cover pan and cook, stirring occasionally, for 30–35 minutes, or until potatoes are tender. Stir parsley and olives into casserole and leave to cool slightly. Transfer casserole to an airtight container and freeze.
To reheat: Transfer casserole to fridge and leave to thaw for a day (or overnight). Place thawed casserole in a shallow microwave-safe dish, cover and microwave on 50% power, stirring once, for 8–10 minutes, or until hot.
To serve: Prepare couscous in a medium bowl according to packet instructions; fluff with a fork to separate grains. Divide couscous among 4 bowls and top with casserole; garnish with extra parsley and serve with a lemon wedge or two.