I don't know anything about Overcooked or working in 3D, but if you want to finish a game in under a month, you probably need to have the basic gameplay prototyped in a week or two. Some genres are just more complicated to program than others. Browsing some game jam entries might give you an idea of the type of games that people make very quickly.
I work (I think) relatively slowly, and all of the finished games in my profile took 1-2 weeks to develop, except MM0, which took two months. This one was far more complex than the others, but is still fairly bare-bones by RPG standards. For that one, implementing the rules, mechanics, and GUI took about half the time, and the content and some basic polish and playtesting took the other half. I still spent a lot of time after the initial jam period adding more features, polish, and fixes. If I had to do it again in half the time, I would probably slash the RPG mechanics to the bare minimum to create a more arcadey experience.