Trim the top off the aubergine and dice the aubergine into small chunks. Peel the red onions and thinly slice them. Peel the garlic cloves and crush or finely chop them.
Pour 1 tbsp olive oil into a large frying pan or skillet and warm to a medium-high heat for 2 mins. Add the meatballs and fry for 4-5 mins, turning once or twice, till browned. Scoop the meatballs out of the pan and onto a plate.
While the meatballs are frying, tip the couscous into a heatproof bowl or small pan. Pour over 300ml boiling water. Cover the bowl with a plate and set aside for 15 mins to soak.
Once you have scooped the meatballs out of the pan and set them aside, reduce the heat under the pan slightly and slide in the chopped aubergine and red onions. Sprinkle in a pinch of salt and pepper. Fry for 10 mins, stirring occasionally, till softened. Stir in the chopped garlic and continue to fry for a further 2 mins.
Pour the passata into the pan, along with 100ml boiling water. Return the meatballs to the pan and stir well. Bring to a simmer, pop on a lid and cook for 10 mins, stirring occasionally, till the meatballs are cooked.
While the meatballs simmer, pick the leaves off the oregano sprigs and set aside.
Add the spinach leaves to the meatballs and stir till wilted. Add most of the oregano leaves. Grate in the lemon zest. Stir to mix. Taste and add more salt and pepper if needed.
Fluff up the couscous with a fork. Squeeze in a little lemon juice and stir well. Spoon the couscous onto 2 warm plates and top with the meatballs and sauce. Serve with the salad leaves and the yogurt on the side, garnished with the last of the oregano leaves.