In a large cast iron skillet, warm the oil over medium-high heat. Add onions and cook until translucent. Add green chilies and cook for about 2 minutes.
Add evaporated milk. Once it begins to simmer turn to low heat and add the shredded cheese in batches while stirring consistently. Once each batch of cheese melts, add more cheese and continue to stir consistently until cheese is melted.
Once all the cheese is melted stir in the Rotel, salt, black pepper, and cumin. Fold in cilantro.