If you're adding a cream layer (can be found in this recipe here), then place the tart in the freezer for at least 15 minutes after adding the lemon filling to it. Use that time to prepare the coconut cream. Remove the tart from the freezer and carefully spread the cream layer and then place back in the fridge (or freezer) to set properly. Placing the lemon-filled tart in the freezer prior to adding the cream layer helps the two layers not to mix together and makes it easier to spread the whipped topping.
You can make this lemon tart without the soy for those on a soy-free diet. You can simply omit the soy from the crust. I've made it like that for another recipe and it worked and tasted just fine, though I found it cracked ever so slightly during baking, so be sure to pierce lots of holes with a fork to prevent bubbling ({and hence cracking}. It really didn't alter things though and was so minor that you won't notice once the tart is filled. As for the soy in the filling, I recommend pre-soaking about ¾ cup raw cashews and then blending them into a smooth consistency along with the rest of the ingredients in place of the tofu.