1Prepare the sauce: In a food processor, combine canned tomatoes, onion, garlic, red wine vinegar, cumin, oregano, ground cloves, paprika, and salt and pepper to taste. Process until smooth.
2Season the flank steak with salt and pepper, and then sear it in a hot pan until browned on both sides.
3In a large pot or Dutch oven, combine the seared steak with the sauce prepared previously. Add bay leaves and a cinnamon stick. Cover with water or broth and bring to a simmer.
4Place the pot in a pressure cooker, seal, and cook according to the manufacturer's instructions (usually around 30-45 minutes).
5Make the pickled onions: Slice a red onion and submerge it in boiling water with vinegar, sugar, salt, peppercorns, and a clove of garlic for 10-15 minutes.
6Make the avocado crema: In a food processor, combine avocados, sour cream or yogurt, garlic, lime juice, cilantro, jalapeño, and salt. Process until smooth and creamy.
7Shred the cooked beef and remove the bay leaves and cinnamon stick. Warm the corn tortillas in a pan.
8Assemble the tacos: Place shredded beef on a warmed tortilla, top with pickled onions, avocado crema, and extra cilantro. Serve immediately.