What's a good, non-liquid substitute for lemon juice?

One of my favorite things to make is the Mint Yogurt sauce from Kokkari in San Francisco, and its sister restaurant Evvia in Palo Alto.

I've been following the recipe in the cookbook and it produces an end result on par with the one served in the restaurant as a companion to the zucchini cakes.

I'd to make an even better version. My goal is to thicken it up by replacing the lemon juice with something dry such as lemon zest. Would this be a suitable replacement? FYI, the yogurt has been drained to a very thick consistency.

I love to know if it would create a similar result in terms of flavor, and also if there are other options that come to mind.