Place the shallots, garlic and chicken breasts in the base of a tagine or a large, heavy-based saucepan and scatter over the fennel and cumin seeds and dried mint. Pour in just enough water to cover the chicken and drizzle in the oil. Bring to the boil, then reduce the heat, cover and cook gently for 40 minutes.
Stir in the vinegar and courgettes and season with salt and pepper. Re-cover and cook gently for a further 15–20 minutes until the courgettes are tender and the flavours have mingled. Garnish with the fresh mint and serve with couscous, if liked.