The precise spice combination varies. It's somewhat similar to taco seasoning, but fajita blends usually have a few extra spices and generally don't include the cornstarch that's often used as a thickener in taco blends. As an example, our basic, "classic" Homemade Fajita Seasoning includes 8 ingredients (garlic powder, chili powder, cumin, onion powder, salt, paprika, black pepper, and oregano), which is perfect for our Shrimp Fajitas. Not all of those spices are needed, though, in the simplified spice mixture we use in this casserole recipe (since we're already packing in Mexican flavor from the jar of salsa).