1. Season and brown lamb: 
In a small bowl, stir together all of the American lamb rub spices. Reserve about a third of the spice mix to use after pressure cooking. Trim excess fat from the lamb leg and sprinkle with the seasoning blend. Turn the instant pot to saute mode and add the olive oil. Brown the lamb leg on all sides turning every couple of minutes until nicely browned.

2. Cook and shred lamb:
Add a splash of broth to the pot to deglaze, scraping up the browned bits. Add tomato paste, remaining broth, garlic, vinegar, and onion. Stir to combine. Return lamb to the pot. Lock the lid and set to Pressure Cook (High) for 2 hours. Natural release for 20 minutes, then manually release any remaining pressure. Remove the lamb and place into a large bowl and let rest for 10 minutes. 

Shred using two forks or in the bowl of a stand mixer using the paddle attachment. 

3. Make quick pickled cabbage: 
Place the cabbage, onion, and carrot (if using) in a medium bowl or jar. In a small saucepan, combine vinegar, water, honey (or sugar), salt, peppercorns, mustard seeds, garlic, and red pepper flakes. Bring just to a simmer, stirring to dissolve the honey or sugar. Pour the hot brine over the cabbage mixture. Press down so everything is submerged. Let it sit at room temperature for 20–30 minutes (or longer). For even better flavor, chill for an hour or overnight. 

4. Crisp lamb: 
Sprinkle remaining spice mixture over the shredded lamb. Heat a large skillet (preferably cast iron) over high heat with about 2 Tbsp of olive oil. Add the lamb in batches so as to not overcrowd the pan and drizzle about 3 tbsp of the roasting juices from the instant pot over the shredded meat. Cook without stirring for about 2-4 minutes or until the juice has evaporated and the meat has a nice golden brown and crispy crust. Flip and brown on the other side. Repeat with remaining lamb.

5. Assemble: 
In a small bowl, whisk together the mayo, garlic, dill, mustard, and lemon juice. Add salt and pepper to taste. Slather sauce generously on both sides of toasted bread. Use tongs to pile on shredded lamb and top with the pickled cabbage.