Place a large sauté pan, for which you have a lid, on a high heat. Add the orzo and toast for 10 minutes, stirring very frequently. Tip the toasted orzo into a bowl and set aside.
Return the same pan to a medium heat and add the olive oil and onions. Cook for about 8 minutes, stirring a few times, until the onions start to turn golden. Add the spinach, in batches, stirring each batch un