Cook onion in butter over moderately low heat in a saucepan, stirring occasionally
until onion is softened. Add chiles and tomatoes. Cook mixture 8 to 10 minutes
over moderate heat until liquid evaporates, stirring occasionally.
Stir in cream cheese. Maintain moderate to low heat until the cheese melts.
Stir in chicken broth, half-and-half, lemon juice, cayenne pepper and salt.
Heat soup over moderate heat until hot, but do not boil.
Sprinkle the tortilla chips, green onions, and Monterey jack cheese over