Step 1Wash the California, ancho and chiles de arbol in a saucepan and add the water. Partially cover the pan and boil the chiles about 8 minutes. Remove the pan from the heat and let the chiles stand 10 to 15 minutes.
Step 2Remove as many chile stems as possible. Place the chiles and liquid in a blender, add the garlic and blend at medium speed 2 to 3 minutes. The sauce should be very smooth and have an almost watery texture. Add salt to taste.
Step 3Heat the oil in a clean saucepan over medium-high heat. Add the sauce and boil about 10 minutes. Keep the sauce warm.
Step 1Combine the cheese and onion and set aside.
Step 2Heat the oil in a skillet. When the oil is very hot, lift a tortilla with tongs and place it in the oil for 4 seconds a side. Submerge each tortilla in the warm sauce briefly, working with your hands or tongs. Place a tortilla on a plate, spread about 2 tablespoons of the cheese mixture on top and roll. Place on a serving platter. Repeat with the tortillas until all the enchiladas are completed, then sprinkle them with the remaining cheese, about 1/2 cup.