I also have a leopard, he/she is about 19 months old. I have had him for 14 months. He loves timothy grass, orchard hay, whatever. Like the others who have replied I mix in other stuff but I try to make sure about 75% is the grass. Of course in the winter here (8 months of the year I cannot give yard grass). I do have potted plants like hibiscus, ficus, and a coule others that I forget the names of. I toss in a leaf or two from those and the most important part is that I soak the dried grass for 15 minutes or so and then chop it up real good. I never toss in letuce because I really know nothing about torts except what I read and all the "experts" seem to say no kitchen greens like lettuce for leopards. I also soak a couple mazuri every two to three days and chop that with the grass. His favorite is cactus pad (which has good fiber) that I just get from the local grocery store - and I chop that in as well.
My personal opinion is that soaking the grass and chopping it gives it a lot more flavor and smell. I cannot imagin that dry grass would be appealing to any tort unless they were nearly dead from starvation. When I first got him many times I gave him only soaked and chopped timothy/orchard grass. He didn't have any choice but to get to like it. Tough love!