Mix together the Marmite and soft cheese in a bowl, then spread over the white bread. Cover with the brown bread and press together firmly. Using a medium-sized cutter, cut out as many flower shapes as you can.
Cut a small circle out of the centre of each sandwich using an apple corer and stick either a cherry tomato half or grape half in the middle.
Arrange on a plate or board on a bed of mustard and cress. Cut small flower shapes from the carrot slices using a small cutter and scatter over the 'grass'.