Step 1

Heat the oven to 350°F with a rack in the lower-middle position. In a large Dutch oven, stir together the pork, 1 teaspoon salt, 1 habanero, half the onion, the garlic, fennel seeds, oregano and 2 cups water. Cover and transfer to the oven and cook until a skewer inserted into the pork meets no resistance, about 3 hours.

Step 2

While the pork cooks, in a blender, combine the orange juice, the remaining habanero and achiote paste. Blend until smooth, about 1 minute; transfer to a medium bowl, cover and refrigerate until ready to use.

Step 3

When the pork is done, remove the pot from the oven. Using a slotted spoon, transfer the meat to a large bowl. Tilt the pot to pool the cooking liquid to one side and use a wide spoon to skim off as much fat as possible from the surface; reserve the fat. Bring the liquid to a simmer over medium and cook, stirring occasionally, until reduced to about ¼ cup, 5 to 7 minutes; remove from the heat. Shred the meat, discarding any bits of fat and gristle; set aside.

Step 4

In a 12-inch nonstick skillet over medium-high, heat 2 tablespoons of the reserved pork fat until barely smoking. Add the remaining onion and cook, stirring occasionally, until lightly browned, 5 to 7 minutes; transfer to a small bowl and set aside. Add another 1 tablespoon of the reserved pork fat to the skillet and heat over medium-high until shimmering. Add the shredded pork and cook without stirring until browned and crisped on the bottom, 5 to 7 minutes. Stir and cook, stirring occasionally, until well browned, another 5 to 7 minutes. Remove from the heat.

Step 5

To the reduced cooking liquid in the Dutch oven, add the orange juice-achiote paste puree. Bring to a simmer over medium and cook, stirring occasionally, until the mixture is thick enough that a spatula drawn through it leaves a trail, about 5 minutes. Stir in the sautéed onion and the browned pork; cook, stirring often, until the pork is evenly coated and heated through, 2 to 3 minutes. Off heat, stir in the cilantro and lime juice. Taste and season with salt and pepper. To serve, transfer the pork to a serving bowl, then serve with the tortillas and the pickled red onions for making tacos.