Preheat the oven to 450°F and arrange a rimmed baking sheet for the taquitos.
If using chorizo: heat a large skillet over medium-high. Add the ground chorizo and the chopped yellow onion and cook, breaking up the meat, until the chorizo is browned and the onion is softened, about 8–10 minutes. Drain off any excess grease. If not using chorizo: heat the skillet over medium-high, add the chopped yellow onion, and cook until softened, about 4–6 minutes; proceed to the next step.
Remove the skillet from the heat and stir in the seeded, finely chopped poblano and the finely chopped chipotle chile in adobo. Set the chorizo/poblano mixture aside to cool slightly.
In a bowl, combine 1 cup shredded sharp cheddar, 1 cup cubed Monterey Jack, and 1/2 cup shredded mozzarella. Mix to distribute the cheeses evenly.
Warm the tortillas (16–20) in the microwave for 30 seconds to 1 minute, until pliable.
Assemble the taquitos: working with one warmed tortilla at a time, spoon 1–2 tablespoons of the cheese mixture in a line down the center. Add a sprinkle (about 1–2 tablespoons) of the chorizo/poblano mixture over the cheese (omit this step if you did not cook chorizo). Roll the tortilla tightly and place seam-side down on the prepared baking sheet. If needed, press some of the chorizo/poblano mixture into either end of the roll to better enclose the cheese. Repeat with the remaining tortillas and fillings.
Bake the taquitos on the baking sheet in the preheated oven for 5–8 minutes. Turn each taquito over and bake an additional 5 minutes, or until the cheese is melted and the tortillas are crisp.
While the taquitos bake, make the avocado crema: in a blender or food processor, combine the flesh of the 2 avocados (scooped from the halved avocados), 1/2 cup fresh cilantro, 1 grated clove of garlic, the juice from 2 limes, and flaky salt to taste. Blend until smooth and creamy; adjust salt if needed.
Serve the taquitos hot, topped with or served alongside the avocado crema and any desired accompaniments from the ingredient list (yogurt, additional cilantro, salsa, shredded lettuce, and pickled onions).