Preheat oven to 375°F (190°C) and grease a 9x13 inch baking dish.
In a large skillet over medium-high heat, brown the ground beef and onion in vegetable oil until beef is fully cooked. Drain excess grease.
Add garlic, cumin, chili powder, and salt to the beef; cook for 1 minute until fragrant.
In a blender or food processor, combine sour cream, mayonnaise, cilantro, lime juice, and milk. Process until smooth and bright green.
Warm corn tortillas in the microwave for 30-45 seconds between damp paper towels to prevent cracking.
Spread 1/4 cup of the cilantro sauce on the bottom of the prepared baking dish.
Fill each tortilla with approximately 3 tablespoons of beef mixture and 1 tablespoon of cheese. Roll tightly and place seam-side down in the dish.
Pour the remaining cilantro sauce over the rolled enchiladas and sprinkle with the remaining cheese.
Bake for 20 to 25 minutes until the sauce is bubbling and the cheese is lightly browned.
Let rest for 5 minutes before serving.