Diced avocado, crumbled cotija, diced white onion, sliced radishes and shredded cabbage, for topping
Heat the olive oil in a straight-sided skillet over medium heat. Add the onions and cook until softened, about 4 minutes. Add the garlic and green chiles, and cook until sizzling, about 1 minute. Add the chile powder, cumin, smoked paprika, coriander, oregano and a pinch of salt; stir to coat the onions in the spices. Cook for about 1 minute, then add the tomato sauce, brown sugar and 1 cup water. Bring to a simmer and cook for 5 to 6 minutes.
Add the chicken to the sauce; continue to simmer and reduce until the sauce coats the chicken and is no longer soupy, about 5 minutes.
Fill the Seasoned Taco Shells with the chicken mixture and top with avocado, cotija, onions, radishes and shredded cabbage.
Seasoned Taco Shells:
Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper.
In a small bowl, combine the cumin, chile powder, coriander and 1/2 teaspoon salt.
Arrange the taco shells in a single layer on the prepared baking sheet. Lightly brush the shells inside and out with vegetable oil, and sprinkle all over with the spice mixture. Bake until golden, about 5 minutes, turning once halfway through.