Season the lamb leg steaks with the spices and a pinch of black pepper on both sides and set aside.
Heat the oil in a large non-stick pan over moderate heat until hot. Cook the lamb for 3 to 4 minutes on each side until golden brown. Remove the steaks from the pan and set aside to rest.
Reduce the pan heat to medium. To prepare the sauce, add the tomatoes and garlic to the pan and cook for 2-3 minutes, stirring gently until the tomatoes begin to soften and burst. Season, if required.
Add the butter beans, 2 tablespoons of the reserved bean liquid, and the fresh thyme leaves. Reduce the pan heat and simmer gently for 4 to 5 minutes, stirring occasionally until the sauce is reduced, and the beans and tomatoes are glossy.
Return the lamb to the pan and warm through for 1 to 2 minutes.
In a small bowl, mix together the yogurt and the lemon zest and juice.
Spoon the butter bean and tomato mix equally onto the base of two serving plates. Slice the lamb and arrange over the tomatoey beans. Top with the lemon yogurt and garnish with the herbs of your choice. Serve with crusty bread.