Preheat the oven to 325°F.
To make the carne asada, add the stock, tomatoes, chipotle peppers, onions and garlic to a Dutch oven and stir to combine.
Combine the cumin, chili powder, salt, and black pepper in a small bowl. Sprinkle the spice mixture over the beef so that it is evenly coated.
Put the seasoned beef into the Dutch oven and cover. Braise in the oven until the meat is fork tender, about 3 hours.
Remove the beef from the pot and put it into a baking dish. Shred with 2 forks and drizzle with some of the braising liquid to keep the meat moist. Cover with aluminum foil until ready to serve.
* One of the great things about the chipotle peppers (and there are so many great things) is that you can fresh canned for this recipe. If you go with canned, place the leftover peppers in a resealable container and keep them in the refrigerator for later uses. You can always add the remaining peppers to sour cream or mayo as a spread for sandwiches, or use them in your favorite vinaigrette.
To make the salsa, preheat the broiler. Place the poblano peppers on a sheet pan under the broiler for 8 minutes, turning every 2 minutes until the skins are charred.
Remove the pan from the broiler, transfer the peppers to a bowl, cover with plastic wrap, and let sit to allow the skin to separate from the flesh, about 10 minutes.
Core, seed, and peel the charred skin from the peppers.
Combine the peppers with the remaining salsa ingredients in a blender, holding three-quarters of the diced avocado in reserve. Puree the mixture until smooth.
Pour the salsa into a medium bowl and add the remaining diced avocado. Gently toss the salsa with a rubber spatula to coat the avocado. Taste and adjust the seasonings with more salt and pepper, if desired. Set aside.
To make the tacos, heat the canola oil in a large skillet over medium heat until it reaches 350°F.
Fry the corn tortillas in batches until crispy but still slightly pliable, about 2 to 3 minutes. Transfer them to a sheet tray lined with paper towels to grain any excess oil.
Place the flour tortillas in a damp towel and microwave for 45 seconds on high to soften them.
Arrange a fried corn tortilla on each flour tortilla. Spoon some of the beef on to the corn tortilla. Top with shredded cabbage, 2 tablespoons green salsa, and 1 tablespoon queso fresco.
Repeat with the remaining ingredients. Arrange on a serving platter and serve.