Step 1Place pork, cilantro and onion in large stockpot with water to cover and cook over medium heat until pork is very tender, about 2 1/2 hours.
Step 2Remove pork from stockpot and cut into 1/2-inch pieces. Set aside.
Step 3Place green chiles, and tomato in bowl and mix thoroughly.
Step 4Soak husks in sink filled with warm water 15 minutes. Remove and pat dry. Stack in pile.
Step 5For each tamale, take a spoonful of masa and spread on corn husk, making sure that tapered end of husk points down and that there is room all around the husk to allow for wrapping. Place a spoonful of chopped pork in the center, add some cheese and 1/2 teaspoon chile mixture. Fold in each side of husk, then fold up from bottom. Set aside. Repeat to make rest of tamales.
Step 6When tamales are all formed, place in batches in steamer set over simmering water. Steam until masa is firm, about 1 1/2 hours.