What is Greek seasoning?

I'll second and third the "Cavanders" which is one of the few spice mixes I purchase.

it's very good to make a dressing if you start with a base of that oil and vinegar. You'll have a basic dressing..maybe a touch of lemon. A base.
Mix with some ketchup, sugar, mayo and you'll have a creamy russian/french dressing. (add dill pickle cubes for thousand island).
Take that first base dressing and add sour cream, mayo, thin with buttermilk (or milk) and add dried parsley flakes and onion powder for a ranch.
Cavanders...Yogurt and cucumbers makes a good Tazaki sauce too. (well, good not a great one)
And so, on and so on.
Great to keep on hand IMHO for a quick dressing mix or seasoning a fish or chicken for frying.

Here in Atlanta, GA , there is a brand called Cavender's All Purpose Greek Seasoning. The ingredients listed are Salt, Black Pepper, Garlic,Oregano, Sugar, Onion Powder, Parsley and 5 other spices that they don't list. S-C Seasoning Co, Inc. P.O. Box 1296 Harrison, Arkansas. 72601.

You could just at easily mix something similar on your own if you can't find it. Hope this helps.

Cavender's makes one which is excellent. I posted a recipe for Greek Grilled Lamb Chops which includes a recipe for Greek seasoning. You can find it here:
http://www.food52.com/recipes/12119_grilled_lamb_chops_greek_style

I don't remember where I found it, but here's a recipe: Stir together 2 Tb salt, 1 Tb black pepper, 2 Tb granulated garlic, 2 tsp basil, 2 tsp oregano, 1/4 tsp thyme.

There a lot of different variations, but I think you need to have oregano, mint, thyme, and marjoram, at the very least. Maybe even basil. But the mix definitely needs to have oregano and mint.