Rather than buying fajita seasoning, its easy to make your own. If you are simply going to rub on the mixture before grilling it, omit the cornstarch.

3 Tbsp. cornstarch
2 Tbsp. chili powder
1 Tbsp. salt
1 Tbsp. paprika
1 Tbsp. sugar
2-1/2 tsp. crushed chicken bouillon cube
1-1/2 tsp. onion powder
1/2 tsp. garlic powder
1/2 tsp cayenne pepper
1/4 tsp. crushed red pepper flakes
1/2 tsp. cumin

Combine all of the ingredients in a small bowl. Pour into small glass or plastic container, seal tightly and store in a cool, dry place.