For the Tomatillo Sauce

1. Heat the oil in a medium saucepan over medium heat. Add the onions and garlic and cook, stirring occasionally, until softened, about 5 minutes. Add the tomatillos, jalapeños, sugar, salt, cumin and ⅓ cup water; bring to a simmer, then reduce the heat to medium-low and simmer until tomatillos are softened, about 8 minutes. Transfer the mixture to a blender and purée until completely smooth. Set aside.

For the Filling

1. Place the chicken tenderloins in a medium bowl and sprinkle with the cumin, smoked paprika and salt. Toss with tongs until the chicken is evenly coated with the spice blend.
2. Heat the oil in a large nonstick sauté pan until shimmering but not smoking. Add the chicken and cook until just done, about 2 minutes per side; transfer to a plate to cool. Do not rinse the pan. Add the onions and reduce the heat to medium. Cook, stirring occasionally, until soft, about 5 minutes. Remove the pan from the heat.
3. Once the chicken is cool enough to handle, shred it into bite-sized pieces. (All tenderloins have a tough tendon running through them; just remove it.) Add the shredded chicken to the pan with the onions, along with the chopped cilantro and shredded cheese.

To Assemble

1. Preheat oven to 400 degrees.
2. Spread ¾ cup of the tomatillo sauce on the bottom of a 9 x 13-inch baking dish.
3. Pour the oil into a small bowl or ramekin. Using a pastry brush (or your hands), brush both sides of each tortilla with oil, then stack them on a plate and microwave until hot and steamy, 1½ - 2 minutes. This makes them pliable.
4. Spoon about ⅓ cup of the filling down the center of each tortilla. Roll each tortilla tightly and place side by side in the baking dish, seam side down.
5. Pour the remaining chili sauce over the top, and use the back of a spoon to spread evenly over each tortilla. Sprinkle the cheese down the center of the enchiladas. Bake until hot and bubbling, 15 to 20 minutes. Sprinkle the smoked paprika down the center of the enchiladas and serve immediately with sour cream, lettuce, avocado and lime wedges.
6. Note: If you touch the seeds of the jalapeño pepper, avoid touching your eyes and wash your hands well afterward.
7. Make-Ahead/Freezer-Friendly Instructions: The enchiladas can be assembled up to one day ahead of time, tightly covered with foil, and refrigerated until ready to bake. Allow a few extra minutes in the oven if baking from cold. The cooked enchiladas can be frozen for up to 3 months. When ready to serve, defrost them in the refrigerator for 24 hours and then reheat, covered in foil, in a 325°F oven until hot.