Place roast, 2 C water and salt and pepper into slow cooker and cook on low for 6-7 hours or until meat falls apart and shred easily.
Combine garlic, oil and cumin in bowl.
Combine juice and zest in another bowl.
Heat 1 tsp oil in skillet on high.
Add onion and 1/4 tsp salt and cook until onions are golden brown.
Add in 1/2 C water over onions and cook until liquid evaporates.
Remove onions from pan.
Add in 1 1/2 tsp oil into pan and heat
Add beef and cook until edges are crisp, about 2-4 minutes
Reduce heat and move meat to edges of pan and add in garlic mixture in the center, stir and cook until fragrant and golden brown, about a minute or so.
Remove from heat and add in juice mixture and onion.
Stir to combine.
Season with salt and pepper to taste.