Preheat the oven to 180°C (350°F). In a large casserole dish, melt the butter over low heat. Add the finely diced shallots and sauté, stirring occasionally, for approximately five minutes until they soften slightly.

Incorporate the minced garlic, lemon juice, and zest into the shallots, stirring well to combine. Add the orzo and toss it in the buttery mixture until evenly coated.

Pour in the chicken broth, bringing the mixture to a simmer. Position the poussin on top of the orzo, brushing the chicken with olive oil. Generously season with salt and pepper, and sprinkle thyme over the chicken.

Transfer the dish to the oven and roast for about 45 minutes, checking occasionally to ensure the pan does not dry out. If necessary, add more liquid. The poussin is fully cooked when it reaches an internal temperature of 75°C (167°F) and the juices run clear.

After roasting, allow the poussin to rest for 10 minutes. Taste the orzo for seasoning, adjusting with salt, pepper, and a little more lemon juice if needed. Garnish with chopped spring onions, parmesan, and extra lemon zest.

Serve the poussin by halving it and placing it alongside the orzo, or cook one poussin per person for a more substantial serving.