Preheat oven to 375 degrees F.
Brown the ground beef and onion in a skillet over medium heat until beef is crumbled up and no longer pink. Drain fat and return skillet to stove top.
Add in the chopped green chilies, taco seasoning, and water. Stir until combined and the water is absorbed. Remove from the heat.
Cover the bottom of a 9x13" casserole or baking dish with enchilada sauce (1/4 - 1/2 of the sauce) to evenly coat the bottom of the dish. Reserve the remaining sauce for later.
Spoon about 1/3 cup of the ground beef mixture in a straight line in the center of each tortilla.
Add about 1/4 cup of the shredded cheese on top of the beef mixture and roll up tightly.
Lay the rolled enchiladas seam side down in the casserole dish. Repeat with remaining tortillas, filling up the dish. If you have any beef mixture left over, just sprinkle it over the top of the rolled enchiladas.
Pour the rest of the enchilada sauce over the top of the tortillas, making sure to spread it evenly to coat each tortilla.
Sprinkle all of the remaining cheese over the top of the tortillas. Top with diced green onions if desired.
Bake for 25 minutes or until the center is bubbly.
Top with your favorite toppings and enjoy!