Add the onions and jalapeño to the saucepan, and sauté until tender. Add in the cumin and stir.
Reduce the heat to medium-low, and stir in the heavy cream, cream cheese and Monterey jack cheese. Stir and simmer until the cheese has melted completely.
Mix the tomatoes and ½ the cilantro into the saucepan and salt and pepper to taste.
Stir to combine, and serve immediately with the remaining cilantro as garnish.