Preheat your sous vide machine to 575 degrees Fahrenheit.
Remove string or elastic binding from the lamb's belly. If there is any & flatten the lamb breast, & score it in several places on both sides. This will help the marinade penetrate better and give it more flavor. Put it in a vacuum seal plastic bag. Place in an sous vide machine. Place the lamb in the preheated machine and set the timer for 12 hours. When it’s done turn off the machine.
Make the spice by peeling and finely chop the garlic cloves. In a medium bowl, mix together the chopped garlic with the Ras-El-Hanout, coriander seeds, cumin seeds, thyme leaves, sweet paprika, and olive oil.
Take out the lamb from the machine. Rub the marinade all over the lamb breast and season with salt and pepper.
Add a thick slice of butter to the pan. Baste the lamb with some of the melted butter before returning it to the oven to continue cooking.
While the lamb is roasting, make the couscous. Place 375 ml of hot water or broth in a medium saucepan and bring to a boil. Once boiling, add the couscous. Reduce the heat to low and simmer for 8-10 minutes until cooked through.
To serve, spoon the couscous onto a large serving platter, top with slices of lamb breast and sprinkle over some of the fresh herbs.