Heat the oil in a large, heavy pan. Add the onion, gently fry for 5 mins until softened, add the chicken, then fry until lightly coloured. Add the potatoes, stock and plenty of freshly ground black pepper, then bring to the boil. Cover, then simmer for 30 mins until the potatoes are tender and the chicken is cooked. Can be frozen at this point.
Add the broccoli, spring greens, petit pois and spring onions, stir well, then return to the boil. Cover, then cook for 5 mins more, stir in the pesto and heat through.