To roast the chili peppers, broil, turning occasionally with tongs and leaving the oven door ajar to allow steam to escape, until the skins are blackened all over. Transfer to a bowl, cover and let cool. Peel, seed and chop.
Heat a drizzle of olive oil in a skillet. Add the chorizo and cook, crumbling with a wooden spoon, until browned. Drain off the fat.
Arrange the bread in a casserole dish. Top with the chorizo and then the roasted chilies.
Whisk together the milk, butter, hot sauce and eggs in a bowl and sprinkle with salt and pepper; pour over the chili peppers. Top with the cheese. Cover and refrigerate at least overnight and up to 2 days.
To serve, bring the strata to room temperature and pre-heat the oven to 325°F Bake the strata for 1 hour.
Meanwhile, whizz together the sour cream, avocado and lime juice in a food processor and season with salt and pepper.
Top the strata with tomatoes, cilantro and dollops of the avocado sour cream.