Step one

Soak the lamb in cold water for 5 minutes, then drain and dry thoroughly. Place the lamb in a baking dish and season with 2 teaspoons salt and 1 teaspoon pepper. To make the marinade, whisk together the wine, garlic, allspice, coriander, and tomato paste. Pour the marinade over the lamb and cover. Marinate overnight in the refrigerator.

Step two

Drain the lamb. In a large stockpot, soften the onions in the oil over medium heat for a few minutes. Increase the heat to medium-high and lightly brown the lamb all over for about 5 minutes. Add the wine, garlic, allspice, coriander, tomato paste, and the barley. Add the water and bring to a boil; then lower the heat and simmer, covered, for about 1 1/2 hours, until the barley and lamb are tender.

Step three

Add the rhubarb and cook for 15 minutes, until the rhubarb is just soft but the pieces are still intact. Season with salt and pepper. Splash each serving with 2 tablespoons lemon juice, a scattering of herbs, and a pinch of red pepper flakes.