In a large saute pan with a lid, saute mushrooms with 1 tablespoon of olive oil over high heat until golden brown (note 2). About 5 minutes. Add half of the minced garlic and season with salt and pepper. Saute for a further 1 minute then remove and set aside.
In the same pan (no need to wash), add remaining olive oil, remaining garlic and onions. Saute for 1 minute then add in chicken over high heat. Spread the chicken into 1 single layer and flip after ~3 minutes to lightly caramelise and brown both sides.
Add orzo and chicken stock. Bring up to a boil then reduce heat to low and cook for ~12 minutes with the lid on. Stirring occasionally to prevent the bottom from sticking.
Add mushrooms back in, stir through then add in silverbeet. Stir through until the silverbeet has softened.
Add heavy cream, parmesan cheese, lemon juice and lemon zest (optional). Mix well, taste, and adjust for salt, pepper or lemon juice to taste. The pasta should be thick and creamy. Add in more water to loosen if preferred.
Turn the heat off. Mix in parsley and serve with extra parmesan cheese and freshly cracked black pepper.