Combine the Base Ingredients
In a small mixing bowl, combine the mayonnaise and sour cream (if using). Stir well until smooth and creamy.
Add the Flavorings
Add the lime juice, chopped cilantro, sriracha sauce, garlic powder, and onion powder to the mixture. Stir until everything is well combined.
Taste and Adjust
Taste the sauce and adjust the seasoning as needed. Add salt and pepper to taste. For a sweeter balance, you can mix in a teaspoon of honey. If you prefer a spicier sauce, add more sriracha.
Chill and Serve
For the best flavor, let the sauce chill in the refrigerator for at least 15 minutes to allow the flavors to meld. Once chilled, drizzle over your fish tacos, or serve as a dipping sauce on the side.