Squash Casserole: Reducing the water content?

I love squash casserole, summer squash or zucchini. I notice when I use the zucchini, there seems to be a much greater water content and it makes it hard to set. The summer squash, although there seems to be less water content, still has a little. The recipe I use calls for boiling the squash first before making the mixture for the casserole.

Any suggestions on when boiling squash, how to reduce the water content? I suppose I could grill them instead? Are there any tricks to be known?