Baking Navmesh at runtime freezes the game for a couple seconds

Hello all, I'm making a 3d game about a monster that pathfinds himself to you in a randomly generated maze. I use this:

 surface.BuildNavMesh();

to bake the navmesh at runtime right after the maze is generated, then once you collect the key in the maze, the rooms switch, requiring me to rebake. This works fine, but the game freezes in place for about two seconds while the navmesh is rebaking. Does anyone know of a way to bake while the game is running, or how to maybe play a short cutscene while this is happening? Any help is always appreciated!