Lamb:

1 (2-pound) boneless leg of lamb
4 tablespoons vegetable oil, divided
1 onion, cut into 6 wedges
1 jalapeno, cut into 4 wedges
3 cloves garlic, chopped
1 teaspoon ground cumin
2 cups orange juice
2 cups chicken broth
Salt and pepper to taste
Pickled Red Onion:
1 red onion, thinly sliced
1 1/2 cups red wine vinegar
1 tablespoon sugar
1/2 teaspoon ground cumin
1/2 teaspoon kosher salt
For serving: corn tortillas, limes, cilantro, radishes and feta.
Heat oven to 325F. Season lamb with salt and pepper.
In a Dutch oven, heat 2 tablespoons oil over medium-high heat. Brown lamb on all sides, about 2 minutes on each side. Set lamb aside. Add onion and jalapeno to pan and sauté until onion is golden. Add garlic and cumin and cook 30 seconds. Add lamb back to pan and pour in orange juice and broth. Bring to a simmer, then cover and place in oven. Let cook until lamb is falling apart. About 3 hours.
Meanwhile, make pickled onions. Place onion in a heatproof bowl. In a saucepan, heat vinegar, sugar, cumin and salt over medium-high heat. Bring to a boil and pour mixture over onions. Let stand while lamb cooks.
When lamb is ready, let stand until cool enough to handle, then shred. Heat remaining oil over medium-high heat, then add lamb and cook, not touching it, until bottom layer is crisp, about 3 minutes.
Build tacos in corn tortillas, topping with lime juice, pickled onions, cilantro, sliced radishes and feta.