Slicing 

Select the Object you want to split >Edit Mode

Select the Bisect Tool under (Knife tool)

Press " A" to  select all the vertices (Orange)

Left Click & Drag to create a line Release to set your line

Press "V" to cut then RIGHT CLICK 

RIGHT CLICK stops the vertices from dragging

Select > Select Loops > Select Loop Inner Regions

TO CLOSE THE OBJECT

Object Mode > Select one of the objects > Shift + Alt and select one of the edge points > Press "F" to fill