Season lamb: In a large bowl, combine lamb shanks, garlic, paprika, oregano, salt, cumin, and 2 tablespoons olive oil. Coat well. Marinate 30 minutes, or overnight.
Brown lamb: Set Instant Pot to Sauté. Add remaining 2 tablespoons oil and brown lamb shanks on all sides. Remove and set aside.
Sauté vegetables: Add onion, carrots, green chili, cinnamon stick, and bay leaves. Cook about 5 minutes, until onions begin to soften.
Deglaze: Add red wine and scrape up all browned bits from the bottom of the pot.
Add liquid + lamb: Return lamb shanks to the pot. Add beef stock.
Pressure cook: Lock lid and cook on High Pressure for 30 minutes.
Natural release: Let pressure release naturally. Remove lamb shanks and set aside.
Defat liquid: Remove cinnamon stick and bay leaves. Pour cooking liquid into a fat separator, then return the defatted broth to the pot with the cooked vegetables.
Blend sauce: Use an immersion blender to blend broth and vegetables until smooth. Turn on Sauté and bring to a simmer.
Thicken: Mix cornstarch and water, then stir slurry into the sauce. Simmer until thickened and glossy.
Serve: Return lamb to the sauce, or plate and spoon sauce over the top. Serve with mashed potatoes, polenta, or grits.