Instructions

1. To make the Cebollas Encurtidas (pickled onions), position rack in oven 4-5 inches from heat and preheat broiler. Cut one of the onions into 1/2-inch slices, reserving the other.
2. Arrange onion slices on a foil-lined baking sheet and broil about 4 to 5 minutes on each side, or until tender and just charred. When cool enough to handle, separate into rings, discarding any blackened pieces.
3. In a medium-sized bowl, combine 1/4 cup grapefruit juice, 2 tablespoons orange juice, 2 tablespoons lime juice, 1 teaspoon garlic and 1 teaspoon crushed oregano. Season to taste with kosher salt and freshly ground pepper. Place onion rings in liquid, cover, and refrigerate 4 to 48 hours.
4. To make an Achiote seasoning, in a small bowl add 1/2 teaspoon kosher salt and 1 teaspoon ground black pepper. To that stir in annatto, remaining teaspoon oregano, cumin, cinnamon and allspice. Rub mixture into entire pork. Place pork in a large dish or a large resealable plastic bag. Chill, refrigerated, 4 to 24 hours.
5. Thinly slice remaining red onion, and place in a 4-to 5-quart slow cooker. Add remaining grapefruit juice, orange juice and lime juice. Stir in remaining garlic and bay leaf and place roast in mixture, on top of the onions. Cover and cook on low-heat setting for 8 to 10 hours or on high-heat setting 4 to 5 hours, or until meat may be easily pulled apart with forks.
6. Meanwhile, make the Chiltomate Sauce by placing tomatoes, vinegar and chili peppers in a blender or food processor. Cover and process until smooth. Season to taste with kosher salt. Transfer mixture to a medium saucepan. Bring to a boil; reduce heat. Simmer, uncovered, for 10 minutes or until sauce is desired consistency. (This step may be done up to 48 hours in advance.)
7. Just before meat is cooked and ready to be shredded, heat an 8-inch skillet over medium-high heat. Brush tortillas lightly with oil. Heat each tortilla, one at a time, in skillet on both sides until softened. Wrap in foil to keep warm.
8. Remove pork from slow cooker. Discard bay leaf and let pork rest until cool enough to handle. Using two forks, pull meat apart into shreds and toss with a bit of juice to moisten but not saturate. (Note: At this point, shredded pork may be returned to cooking liquid and refrigerated 24 hours. Drain and reheat when ready to serve.)
9. To assemble tacos, place shredded meat on center of warm tortilla, top with pickled onions, tomato sauce and queso fresco. Serve.