Taco Stuffed Shells

Preheat your oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish with nonstick spray and set aside.
Bring a large pot of salted water to a boil. Cook the jumbo pasta shells for 2 minutes less than package directions (so they're slightly undercooked/sturdy). Drain and cool under cold running water, then arrange on a towel or tray.
Heat a large skillet over medium-high. Add ground beef and onion. Cook, stirring often, until beef is mostly browned and onions are softened, about 5–6 minutes.
Add minced garlic and taco seasoning to the skillet. Stir well and cook for 1–2 minutes until fragrant and the beef is fully cooked.
Stir in the enchilada sauce. Let the mixture simmer gently for 5–10 minutes until slightly thickened. Remove from heat.
Add 1 cup of shredded cheddar cheese to the beef mixture while still warm. Stir to combine until melted and evenly mixed.
Spoon the cheesy taco filling into each cooled shell (about 1–2 tablespoons per shell) and arrange in the prepared baking dish.
Sprinkle remaining 1 cup cheddar and all the Monterey Jack cheese evenly over the stuffed shells.
Cover the dish with foil. Bake for 15 minutes, then remove the foil and bake for another 15 minutes, until the cheese is browned and bubbly.
Let the shells cool for 5–10 minutes before serving. Garnish with sour cream, cilantro, or guacamole if desired.