I'm filing this very loosely under cooking :-D It's a simple fun thing to do with toast and quite a favourite with my kids. They really like the littlest shapes and eat them first and they even eat the crusts (thought they will still just mine for the soft bits in the biggest slice).
It's great fun to make pictures with the traditional Tangram shapes. They pick out all of the different sized matching triangles and stack them together. It gets them naming shapes, talking about sizes, patterns....highly educational and it also fills tums.
Here is another variation where I cut each each new half in half, particularly useful for my eldest who has just turned 5. We talk about halves and quarters.....but not the smaller fractions yet. I think there is a lot of learning mileage yet left for us in humble toast.