In a mixing bowl, combine mayonnaise, chili powder, horseradish, dried oregano, sweet paprika, teaspoon salt, onion powder, and ground black pepper.
Whisk all the ingredients together until well combined and smooth. If you'd prefer it super smooth, use a food processor or blender.
Taste the sauce and adjust the seasoning according to your preference. You can add more chili sauce or more horseradish for more heat, or adjust the salt and pepper to taste.
Once you're happy with the flavor, transfer the sauce to a serving bowl.
Serve the Bloomin Onion Sauce immediately with your favorite fried appetizers, such as a blooming onion, onion rings, French fries, or chicken tenders. Enjoy!