For the Salsa Roja: Clean the chiles with a damp kitchen towel. Deseed the guajillo and ancho chiles, and cut the stems off the morita chiles.
Place all the chiles in a medium saucepan and add 5 cups of water. Bring to a boil over medium-high heat, then reduce the heat to a simmer and cook for 10-15 minutes or until the chiles are softened.
Meanwhile, add the garlic to a blender along with ¼ cup of the cooking liquid, and blend until smooth. Transfer the softened chiles along with the cooking water to the blender with the garlic mixture.
Add 1 tablespoon of knorr chicken bouillon. Blend the mixture on high speed until smooth. Strain the blended salsa through a coarse mesh strainer into a bowl, discarding any solids. Set aside.
Heat oil in a skillet over medium-high heat until shimmering. Whisk in the chile mixture, add salt and black pepper, and bring to a simmer. Reduce heat to medium-low and cook, whisking frequently, until slightly thickened, about 20 to 25 minutes.
Whisk in vinegar if using. Taste and adjust the seasoning with salt and pepper if needed. Remove from heat, cover, and keep warm.
For the Enchiladas: Adjust the oven rack to the middle position and heat the oven to 450 degrees.
Lightly spray or brush both sides of the tortillas with oil. Stack tortillas, then wrap them in a damp dish towel. Place tortillas on a plate and microwave until warm and pliable, about 1 to 1½ minutes.
Spread ½ cup salsa roja in the bottom of a 13 by 9-inch baking dish. Combine cheeses in a bowl; set aside ½ cup cheese mixture for topping enchiladas.
Dip tortillas in chile sauce to lightly coat both sides. Place ¼ cup cheese mixture across the center of each tortilla, then sprinkle each with 1 tablespoon onion.
Tightly roll tortillas around the filling and lay them seam side down in the dish (2 columns of 6 tortillas will fit neatly across the width of the dish). Pour the remaining sauce over the enchiladas, then sprinkle with the reserved cheese mixture.
Cover the dish with aluminum foil and bake until the sauce is bubbling and the cheese is melted about 15 minutes. Let enchiladas cool for 10 minutes, then sprinkle with remaining onion. Serve.