If you use fresh pasta, and you have enough sauce or liquid to cover them, then there is no need to cook them.
For dried pasta, cook it half way, where it is a little too much "al dente" for eating. If the estimated cooking time indicated on the package is 10 minutes, drain at about 6-7 minutes. The rest will be done while they are being baked in the oven. If you are using lasagne sheets, some of them are bake-able without precooking, but if they are they should be indicated on the package.
But in either case, make sure to cover the pasta with enough sauce.