Preheat the oven to 428°F (220°C/200°C fan).
Start by zesting the lemon. Divide the zest in half and pop into 2 small bowls. Cut the lemon into slices.
Add the harissa paste to one of the bowls and mix well.
Pop the chicken thighs into a large bowl and add the lemon-harissa mix. Season with salt and pepper. Give it a good stir to coat the chicken (you could use your hands, but I don’t recommend that with harissa, as it can really stain!).
Pop the onion wedges and chopped red peppers into a roasting pan and lay the lemon slices on top. Using tongs, place the chicken thighs on top, skin-side up. Drizzle the whole tray generously with olive oil, then sprinkle with sea salt - paying particular attention to the chicken skin (the salt will help it go crispy).
Roast in the oven for about 45-50 minutes, or until the chicken is crispy and cooked through. Give the onions a good stir after 20 minutes, basting with the pan juices, to prevent them from coloring too quickly (you don’t want them to burn and become bitter). If any look like they might, carefully tuck them under the chicken thighs.
Meanwhile, prepare the labneh: Place the labneh in a bowl, add the chives and remaining lemon zest. Season to taste with salt and freshly ground black pepper, and mix well to combine. Set aside.
To serve: Spread the labneh onto a plate. Top with the sliced roasted red peppers, followed by the roasted onions and lemon slices. Add the crispy chicken thighs, then drizzle over the delicious harissa chicken juices from the pan. Sprinkle with freshly chopped chives, scallions, and toasted Marcona almonds.