Trim fat from pork shoulder and cut into 1 inch pieces. Cut one onion into large chunks.
Place pork, onion chunks, garlic, ½ teaspoon oregano, and 1 teaspoon salt in a large sauce pan, and add 6 cups water.
Bring to a boil, covered over medium-high heat. Reduce to medium heat, move the lid to the side so that the saucepan is partially covered, and cook about 1 ½ hours. Occasionally, skim off any foam that accumulates.
Once pork is fork tender, reserve 1 cup liquid, and drain remaining liquid.
Discard onion pieces and shred pork.
Heat oil in a large skillet over medium heat. Chop remaining onion and add to the skillet with the pork and oregano. Cook over medium-high heat until the pork is browned.
Stir in tomato sauce, minced chipotle peppers, bay leaves and reserved cooking water. Simmer until the sauce is thickened. Discard bay leaves.
Baked Tostadas
Preheat oven to 450°F and brush tortillas with a bit of oil and season with salt.
Place in a single layer on a baking sheet and cook about 8-10 or until browned.
Add a generous portion of pork on each tostada and add toppings of your choice.
Notes
Pork can be served over tostada shells, in tortillas, or over cauliflower rice.
Optional - To Fry Tostadas:
Heat vegetable oil in 8-inch skillet over medium heat.
Poke tortillas with a fork and fry until golden and crisp.
Remove from the oil and sprinkle with salt.
Prep meat and sauce ahead of time, and reheat when ready to serve.
Refrigerate pork tacos, covered, for up to 2 days. Freeze leftovers, thaw and reheat in a pan, or the microwave, for a quick lunch or dinner.