Preheat the oven to 350 degrees. Grease a 9×13-inch baking dish with non-stick cooking spray.

Heat 1 tablespoon unsalted butter in a large skillet over medium-high heat. Add 1 pound cremini mushrooms, roughly chopped, and cook until browned, about 5–6 minutes. Transfer the mushrooms to a plate and set aside.

In the same skillet, add 1 pound lean ground beef. Cook, breaking up the meat, until browned, about 8–10 minutes.

Add ½ cup minced onion, 2 ½ teaspoons ground cumin, 1 ½ teaspoons dried oregano, 1 teaspoon salt, and 2 large minced garlic cloves to the beef. Cook until the onions are soft and translucent, about 3–4 minutes.

Return the cooked mushrooms to the skillet with the beef mixture. Add ¼ water and toss to combine. Remove from heat and set the filling aside.

In a medium bowl, whisk together 16 ounces salsa verde and 1 cup sour cream until smooth. Set the sauce aside.

Spoon about 1/2 cup of the sauce into the bottom of the prepared baking dish.

To assemble each enchilada: place about 1/2 cup of the beef-and-mushroom filling in the center of each of the 10 soft taco-sized tortillas. Sprinkle each filled tortilla with about 1 tablespoon of the 8 ounces Oaxaca cheese, shredded. Roll the tortilla and place it seam-side down in the baking dish.

Pour the remaining sauce evenly over the rolled enchiladas and sprinkle the remaining shredded Oaxaca cheese on top.

Bake uncovered for 30–35 minutes, or until the sauce is bubbly and the cheese is lightly browned. Remove from the oven and let rest a few minutes before serving.