Sauce:
3 tablespoons mayonnaise
2 teaspoons fresh lime juice (optional)
Cheese mixture:
2 tablespoons finely grated Parmesan cheese
1/2 teaspoon chili powder
1/4 teaspoon ground red pepper
1/4 teaspoon ground cumin
1/8 teaspoon salt
Alternative versions have a mix of mayo and butter and then a cheese called Cotija which is between a Parmesan and Feta.
Also, some regions do sour cream instead of mayo, but then the lime juice is a bit less optional.