Tap or double tap do undo?

I’m creating a game in a 3×3 board where each move consumes active cells and creates used cell instead. I want users to be able to undo moves, and they have a button alongside other buttons like go to the next or previous level.

But this is UX and I want the undo action to be a gesture too and I don’t know which one is best: tapping a used cell once to undo or double tapping anywhere in the screen that is not interactive, like the background outside the board or, again, used cells.

• Tapping once in the background is too broad.
• Tapping once in a dead cell requires the user to "find" a dead cell. They are clearly visible but their position changes from level to level.
• Double tapping in the background brings to the users a constant interaction across all levels they can quickly rely on. But double tapping is evil, right?