I have been working on a project which also requires, more or less, a webcam with HD quality (something like 720p) and an optical zoom lens. There are such things for sale ... but they are industrial-strength, and industrial-priced, such as pan-tilt-zoom cameras for high-end videoconferencing equipment. And, of course, there are the commercial cameras that the TV broadcasters use. There aren't any such things in the consumer marketplace.
I found one guy who took apart a Sony camcorder and bolted its zoom lens to a standard webcam. He has a video of the process here:
I did about the same thing: I also took the zoom lens out of an old Sony camcorder, and literally bolted it onto the circuit board of a Sony PlayStation "Eye" webcam (good electronics for $40), and "FrankenCam" works fairly well. The image is decent but washed-out. I need to work on aperture control. And I may need a better IR filter.
I found another guy who will sell you a Sony Playstation Eye webcam, installed in a case with a standard lens mount, here:
He also offers a low-pass filter that may help me with my image quality. I may try that if I can't get decent results on my own.
But I still think that we both could instead find an off-the-shelf camcorder, or digital camera, with a 'real-time' image feed. Many cameras and camcorders will support an external "AV feed", but all the ones I've seen, and bought, send out very poor video, usually broadcast-TV quality. I'm still looking for a good camera that will put out real-time HD video. For example, I have high hopes for the new Samsung Galaxy Camera, an Android tablet that thinks its a high-quality camera, which I just started to research.
Update, August 2014:
Here's the status of my project, after a year of window-shopping and experimenting.
My "FrankenCam" described above is working fine, in terms of the original requirements, and with the re-installation of the IR filter from the Playstation Eye camera. But I had two new problems: (1) the only Playstation webcam driver for Windows doesn't work with my 64-bit software stack, and (2) I couldn't reliably get a fast shutter speed, which the OP may not need, but I needed it: my project is video-recognition, in real-time, of race cars on a racetrack, to support a real-time scoring system, and of course I need a very short exposure time to capture a fast-moving race car. So I bought some more hardware: a Panasonic HCV-250 camcorder which puts out 1080p/60fps into a standard HDMI cable, and an AverMedia ExtremeCap U3 Capture Box which converts the HDMI signal into USB3 for my laptop. I looked at a lot of other cameras and HDMI interface boxes, and bought, tried, failed, and returned several. I still don't understand why a $20 webcam can put out a hi-def video signal over USB but a high-quality camcorder cannot ... but that's certainly another question, and off-topic here.
Hope this helps.