Heat the olive oil in a large skillet over medium-high heat.
Add the finely chopped onion and cook, stirring occasionally, until translucent, about 5 minutes.
Stir in the ground cumin, paprika, kosher salt, garlic powder, and dried oregano until the onion is evenly coated and fragrant.
Add the shredded rotisserie chicken and stir to combine with the spices.
Pour in the water, then add the diced chipotle pepper and 2 teaspoons chipotle in adobo sauce from the can; stir until well combined.
Reduce the heat to low and simmer, stirring occasionally, until the mixture thickens slightly, about 3 to 5 minutes.
Warm the corn or flour tortillas, then spoon the chipotle chicken into each tortilla.
Top with desired toppings and serve warm.