Rub shanks with 1 tbsp lemon juice and season. In a skillet, saute shanks in olive oil and sear, turning to brown all sides.
Transfer shanks to a casserole dish and sprinkle with remaining lemon juice, garlic, and oregano. Add onion and bake covered, for 2 1/2 hours.
Add beef broth, wine, and artichoke hearts. raise heat to 350°F and bake covered for 30 minutes more.
Transfer lamb and chokes to a platter to keep warm. Mix cornstarch and water in a cup. On stovetop, Add cornstarch mixture to the casserole dish and cook with the lamb juice on med-high heat to thicken.