A sexual manouvre. When the dominant partner is just about to come, they pin their partner down, and straddle their head, unleashing their load on to their partner's face, thus combining 'cheese' and the act of bundling. (bundle (see definition 5))
Jack: God, I'm nearly there
*tackles Jill to the floor and jumps on to her face -jizz-*
Jill: Oh my God, what was that?
Jack: That, dearest, was a cheese bundle. Now go and clean your face, we've got guests arriving in half an hour.