To make the vinaigrette, whisk together the oil, vinegar, garlic, dried and fresh oregano, thyme, and lemon juice; season with salt and pepper. Pat the lamb dry and place it into a shallow platter. Season it well with salt and pepper. Pour 1/2 the vinaigrette over the lamb and let it marinate for at least 15 minutes or up to 2 hours.
Heat the grill or grill pan and oil it lightly. Remove the lamb from the marinade and grill for about 15 to 20 minutes per side for medium-rare. (Adjust the time accordingly for other degrees of doneness.) Cover and let rest for 10 minutes. Carve into thin slices.
Toss the mache, mint leaves, and scallions in a bowl and season with salt and pepper. Dress the salad with about 3 tablespoons of the vinaigrette and mix well. Place the lamb onto a serving board. To serve, spread the Lemony Chickpea Puree over the lamb and put the greens on top of the puree.
Drain and rinse chickpeas and put them into a saucepan. Cover with cold water by 2 inches; add the bay leaf and salt and bring to a boil. Reduce heat and simmer beans until tender, about 1 1/2 hours. Drain, reserving about 1 cup of the cooking liquid. Remove the bay leaf and discard.
Put cooked chickpeas into a food processor or blender. Add the olive oil, lemon juice and zest, garlic, and salt and pepper to taste. Process until smooth; add some of the reserved cooking liquid to thin, if needed. Serve on top of the Grilled Marinated Lamb or put into a serving dish and garnish with a drizzle of olive oil and the parsley.
If you are concerned if the oils or other ingredients in these recipes are suitable for Passover, seek non-dairy substitutes or ingredients that are certified kosher for Passover.