Preheat the oven to 350 degrees Fahrenheit (175 degrees Celsius).

In a medium pot, add oil and sauté the diced white onions. When halfway cooked, add half of the enchilada seasoning mix. Stir often to prevent burning. Once the onions become soft, add minced garlic and cook for 1 minute. Pour in the tomato sauce and water. Bring the mixture to a low simmer and stir often.

In a large skillet over medium heat, cook the ground beef, breaking it up as it cooks. When halfway cooked, add the diced onions and poblano pepper. Cook until the meat is browned. Add minced garlic, the remaining half of the enchilada seasoning mix, and water. Stir and let it simmer for 10 minutes. Taste and adjust salt and pepper as needed.

Warm up the corn tortillas to make them more pliable (30 seconds in the microwave should be sufficient). Grease a 9x13 baking dish and spread 2-3 tablespoons of the prepared enchilada sauce on the bottom.

Assembly: Dip a corn tortilla in the enchilada sauce, place 1-2 tablespoons of the cooked meat mixture and 1 tablespoon of Colby Jack cheese onto the tortilla, then roll it up. Place the rolled tortilla seam side down into the baking dish. Repeat this process with the remaining tortillas, arranging them snugly in the dish.

Once all the enchiladas are assembled, pour any remaining sauce and meat over the top and then place sliced cheese on the enchiladas.

Bake in the preheated oven for 25-30 minutes, or until the cheese is melted and the edges are bubbly.

Let the enchiladas rest for 5 minutes before serving.