See note 4 for Instant Pot method. Remove the chuck roast from packaging and pat dry with a paper towel. Season with salt and pepper. Heat 2 tablespoons of oil in a large Dutch oven or oven-safe pot over medium-high heat. Sear the beef for 5–7 minutes on each side until a crust forms and it releases easily from the pan. Transfer the beef to a slow cooker.
Reduce heat to low. Add remaining 1 tablespoon oil to the Dutch oven and sauté the diced onion for 3 minutes. Add taco seasoning and cook for 1 more minute. Stir in 20 ounces enchilada sauce, scraping up any browned bits from the pan. Transfer the onion mixture to the slow cooker along with the optional green chiles.
Cover and cook on low for 7–9 hours or on high for 5–7 hours, until the beef is tender and shreds easily. Once cooked, transfer the beef to a large bowl and let it cool slightly. Shred the beef with two forks, discarding any fat. Whisk the sauce in the slow cooker and adjust seasoning if needed. Add 1 cup of the sauce to the shredded beef and, using tongs, gently toss to combine.
Preheat oven to 350°F. Grease a 9x13-inch baking pan and spread 1/2 cup of sauce on the bottom. In a medium bowl, toss together the Cheddar and Monterey Jack. Set aside 1 cup of cheese for topping. Lay out tortillas and spread about 2 tablespoons of refried beans down the center of each. Divide shredded beef evenly on top and sprinkle with remaining cheese. Roll up each tortilla tightly and place seam-side down in the prepared pan.
Pour 2 cups of the remaining enchilada sauce over the tortillas (see note 5). Cover pan with foil and bake for 30 minutes. Remove foil, top with the reserved cheese, and bake an additional 5–10 minutes until cheese is melted.
Let enchiladas rest for 5–10 minutes before serving. Top with your favorite garnishes like cilantro, lime, avocado, or sour cream.
Video
Notes
Note 1: Homemade taco seasoning: Mix 1 tablespoon chili powder, 1 teaspoon cumin, 1 teaspoon paprika, 1/2 teaspoon onion powder, 1/2 teaspoon garlic powder, and 1/2 teaspoon dried oregano.Note 2: For best results, use high-quality tortillas like TortillaLand®. If using unbaked tortillas, cook them in a pan before assembling.Note 3: Optional toppings for serving include fresh cilantro, fresh lime, avocado or guacamole, pico de gallo, and sour cream.Note 4: Instant Pot Method: Sear the beef in the Instant Pot on “sauté” mode. After browning, add the remaining oil and sauté the onion. Stir in seasonings and enchilada sauce. Whisk really well and make sure nothing is stuck to the bottom so you don't get a burn notice. On manual mode, pressure cook the beef for 45 minutes. Allow a natural release for 25 minutes.Note 5: You might have extra enchilada sauce. Don’t reduce the amount—it's needed for cooking the beef. Check the post for ideas on using the leftover sauce!Storage: Store leftover enchiladas in an airtight container in the fridge for up to 3 days. For longer storage, freeze in a freezer-safe container for up to 3 months. Reheat in the oven until warmed through.