Heat oil in a large skillet over medium heat. Add onion, chiles, coriander, and 1 teaspoon salt. Saute, stirring occasionally, until onion and chiles are tender and caramelized, 25 to 30 minutes. Let cool completely.
Stir together lime juice, cream cheese, and sour cream in a large bowl, using a rubber spatula, until smooth. Stir in onion mixture. Season with salt if necessary. Refrigerate at least 1 hour and up to 1 day. Sprinkle with cayenne. Serve with cut-up vegetables or chips.