You will need to kill out the zoysia or it will likely reappear in spots from any left behind rhizomes. Roundup will do the job, however you need to do it while it is still green. About a week later, remove or till the zoysia into the soil. Apply a starter fertilizer and a blend of turf type fescue (not K-31) at a seeding rate of 15 lbs. per 1000 s.f. and lightly till in shallow (1" max.) or hand rake to slightly cover the seed.
Your local nursery or farm center can advise you on TTF varieties and blends for sun/shaded, traffic areas, drought tolerence etc.
You may want to post on the "Lawn Forum" as there are some knowledgeable people there.

If you haven't been there yet, I recommend it too. There's tons of great information and questions are usually answered quickly.