Heat your oven to 190°C/Fan 170°C/Gas 5. Tip the couscous into a heatproof bowl. Pour in 150ml boiling water. Cover with a plate or cling film. Set aside for 10 mins to absorb the water.
Trim the top and bottom off the leek. Halve it and rinse out any grit. Thinly slice it. Heat 1 tbsp oil in a deep frying pan or wok. Add the leek. Season with salt and pepper. Stir and fry for 7–8 mins over a low heat till soft. Take off the heat.
While the leek cooks, halve the peppers lengthways. Scoop out any seeds and white bits. Place on a baking tray, skin-side down. Slide into the oven and roast for 5 mins to soften them up.
Finely chop the tomatoes. Stir them into the leek with a good pinch of dried oregano. Stir in the couscous. Grate in the lemon zest. Taste and add a little salt and pepper if you think it needs it.
Pile the couscous mixture into the pepper halves. Crumble half the pack of feta over the top. Drizzle each with 1 tsp oil. Bake for 10–15 mins, or till the feta is golden. If you have extra stuffing that won’t fit, keep it to serve as a side salad with the stuffed peppers once they’re baked.
While the peppers are in the oven, peel the beetroot (it can stain, so wear gloves if you like, and use a plate instead of a board, or cover your board with baking paper). Dice it and tip into a bowl. Roughly chop half the cucumber and add to the bowl along with the olives. Peel and finely slice the red onion and add to the bowl. Slice the skin and white pith off the orange. Slice the segments out and add to the bowl.
Mix the beetroot, cucumber, onion and orange together. Squeeze in a little lemon juice and season. Serve the peppers with the chopped salad and some watercress on the side, as well as any spare stuffing.