SEASONING: Mix it all together and keep it in an airtight container/jar. Use 2 tablespoons of the seasoning for 1 whole boneless chicken breast. You can always add later some more to please your own taste.
You can slice everything ahead and store it in your fridge for up to 2 days (for chicken), or in the freezer, 0 degrees F or below, up to 9 months for raw sliced chicken according to Storage Times Food Safty Chart and it is generally recommended frozen vegetables to be eaten within 8 months for best quality. Make sure to separate both and pack in individual freezer bags.
As for the Fajita seasoning, I'd recommend to use it for the period of 3 to 4 months. You probably have all the ingredients, so just mix them up, store in the jar and you are good to go. It goes well with turkey, beef, or vegetables if you do not eat meat fajitas.