Stem and seed the chiles and cut into narrow strips. Sauté the onion in vegetable oil until soft and translucent, about 5 to 8 minutes. Do not brown. Add the chiles and cook 1 minute, then add the cream cheese and spices. When the cream cheese is completely melted, add the grated Oaxaca or mozzarella cheese in 6 to 8 handsful. Allow the cheese to melt without stirring and take care to keep the temperature low.

Serve in individual ramekins with a hot flour tortilla draped over the top of each bowl. To eat, the raja mixture is simply spooned into the tortilla, which is rolled or folded to keep the mixture from spilling out. Remember the trick of tipping one end up so you don't lose any of the delicious filling.

The chile and onion mixture may be prepared up to 2 days in advance and either refrigerated or frozen until ready to use. Be sure to reheat it before adding the two cheeses.