I'm wanted to make a lemon garlic chicken in a crockpot and I'd like to serve it with couscous. Is there a way to cook the two together? I know I can cook the couscous and then add it in the crockpot at the end but I'd prefer to avoid using an extra pot. Can I just add extra liquid (broth) and then add it in halfway, or add it in with the chicken right from the start?
I think this is going to be a bad idea; you'll go from ideal couscous texture (fluffy and light) to mush. I have an article (on my blog) about how to make fluffy couscous. The crux is simply to put it, with the appropriate amount boiling water, in a wide, shallow vessel and cover it for 5 minutes. You can even set that up ahead of time, and when you are ready to serve the food from your crockpot, just add the boiling water from a teakettle and you'll be good to go.
If this is the kind of couscous you generally get in the US, the normal method of cooking it is to stir it into boiling water and then remove from heat and cover tightly. That suggests that you should be able to stir it in at the end of cooking your chicken, along with whatever liquid is necessary to bring you to the 1.5:1 ratio. That'd be pretty much the same as cooking it normally, as long as your crockpot lid isn't too loose. If you're cooking the chicken well below boiling, you could make sure the liquid you add is boiling.
Instead of the 5 min / boiling water method, you can also steam couscous, but it's much more work -- Alton Brown's technique calls for steaming, separating the grains, then steaming a second time. Tradiationally' it's cooked in a couscoussier, which is basically a steamer, but has a larger pot underneath so you could cook your main dish at the same time.
If you could fit a steamer above the crock pot, and it was generating enough steam, and you could get the steam to not all escape out the sides ... this could work. But it'd still be something else to clean, so I don't know if you'd want to do it.
If I were going to try to keep it all to one pot, I'd probably pull the chicken, measure out the liquid in the pot, pour it back into the crockpot with any additional liquid needed, turned to high -- heat it 'til it bubbled (which is going to take a while, it's a crockpot) and add the couscous, cover, and let sit for a few minutes (might not be 5 ... you'll have to check it)