Preheat the oven to 200C/400F.
Mix the water, oil, oregano, olives and seasoning in a large baking tin with sides. I used a 1.6 litre 30cm length x 20cm width x 6cm height Le Creuset baking dish. Halve the lemons, remove any obvious pips and squeeze the lemon juice into the mixture. Arrange the 4 lemon halves in the corners of the tin.
Add the potatoes and use your hands to coat them all evenly in the mixture. Place the tin onto a tray if needed (to catch any drips) and into the oven for 40 minutes.
Meanwhile, soak the quinoa for 10 minutes. Once soaked, drain the water and add 500ml (2 cups)* fresh water to the quinoa in a medium saucepan. Season well.
Cook the quinoa, stirring intermittently, until it has absorbed all the water. It should have unfurled nicely. Once it has, cover the quinoa with a lid and allow to steam for 10 or so minutes. Fluff it up with a fork and taste for seasoning (but we will have a built in sauce from the potatoes, so don’t go too crazy).
At the 40 minute mark, flip any browning potatoes and the shuffle the potatoes at the bottom to the top (if needed). This will depend on the size of your tray – they might all be getting heat simultaneously if your tray has enough room (see notes).
Once turned, return your potatoes to the oven for 20-40 minutes. Most of the liquid should be gone and the potatoes should be golden brown. Check on them to ensure they don’t brown too much.
While you’re waiting for the potatoes, combine the ingredients for the Greek salad in a medium bowl. Taste and adjust for herbs and seasoning then set aside.
Once the potatoes are cooked, remove them from the oven. I like to drain off the cooking liquid (aka sauce) straight onto the cooked quinoa. Stir the quinoa to combine. I also like to squeeze the cooked lemon flesh into the quinoa because it is absolutely delicious.
Personally, I like to spoon the Greek salad right over the potatoes and then serve the quinoa as the grain base of the dish.
Leftovers keep well in the fridge for a number of days.