Add the quinoa to a saucepan of boiling water and simmer for about 10 minutes or according to packet instructions until just tender, then drain in a fine sieve.
Make the dressing by mixing the olive oil, harissa, lemon rind and juice and a little salt in a salad bowl. Stir in the hot quinoa and leave to cool, then mix in the cucumber, green pepper, spring onions and frozen peas.
Mix the lemon rind and juice, oil and harissa in a shallow bowl, then add the chicken and toss well. Heat a griddle pan (or ordinary frying pan), then cook the chicken in batches for about 6 minutes, turning until browned on both sides and cooked through.
Stir the mint through the quinoa salad, then top with the warm chicken. Serve warm or cold. Any leftovers can be chilled and packed into lunchboxes the following day.