Heat the olive oil in a large, deep pan over medium heat. Add the diced onion and cook for 3 to 4 minutes until soft and slightly golden. Add the garlic and cook for 1 minute until fragrant.
Add the risoni and stir well to coat it in the oil and onion mixture. Cook for 1 to 2 minutes to lightly toast the pasta.
Pour in the chicken stock and bring to a gentle simmer. Reduce the heat slightly and cook, stirring often, so the risoni does not stick to the base of the pan. Cook for 10 to 12 minutes or until the risoni is tender and most of the liquid is absorbed.
Pour in the cream and bring to a simmer, then add the shredded roast chicken and parmesan. Stir until everything is well combined and the sauce is smooth and creamy. Let it heat through for 3 to 4 minutes.
Add the baby spinach and stir until wilted. This will only take a minute.
Remove from the heat and stir through the lemon zest. Taste and season with salt and pepper as needed. Serve hot, with extra parmesan, lemon wedges, parsley and chilli flakes if desired, to garnish.