Preheat the oven to 180C, 350F, gas 4.
Season the insides of the poussins. Heat the olive oil in a frying pan and gently sauté the onion until it is soft but not coloured. Add the garlic and cook for another 2 minutes and tip into a bowl and leave to cool.
Gently stir in the rest of the ingredients, except for the wine or stock, being careful not to squash the feta too much, and check the seasoning. Stuff the poussins with the mixture and set them in a small roasting tin. Drizzle with a little more oil and season.
Cook in the oven for 50 minutes, or until the poussins are cooked through. (If you pierce them between the leg and the body the juices should run clear, with no trace of pink.) Move them onto a warm serving dish, cover with foil, then insulate with a couple of tea towels.
Put the roasting tin on the hob and add the wine or stock. Bring to the boil while you scrape up all the bits stuck to the tin (you need this flavour).
Boil until you have a flavour you like – it’s better to have thin juices than thicker ones that are too salty – then strain through a sieve. Serve with the poussins, garnished with dill and lemon slices.