In a skillet over medium heat, cook the chorizo until brown and no longer pink in the middle, about 10 minutes. Break the chorizo apart as it cooks. If necessary, drain the excess grease.
Meanwhile, stir together the sour cream and lime juice. Set aside.
Assemble the tacos. Top the tortillas with chorizo, manchego cheese, pickled onions, a drizzle of lime crema, and garnish with cilantro. Serve.
Pickled red onions
Put the thinly sliced onions into a glass, heat-proof jar.
Combine the vinegar, water, sugar, and salt in a small saucepan. Heat over medium-low heat, stirring to ensure the sugar is dissolved.
Pour the warm liquid over the onions. Cool. Let the onions marinate for 20-30 minutes before enjoying. Cover the jar and store in the refrigerator for up to 1 week.
Notes
Mexican chorizo is sold fresh and ground and needs to be cooked before eating. This shouldn't be confused with Spanish chorizo, which is a spicy cured sausage that is sold in links, much like pepperoni, and doesn't need to be cooked before eating.
Pickled onions can be made in advance and stored in the refrigerator.