Add the gelatin to 1 tbsp of water and mix them together, soak it at least 15 min.
Squeeze the juice from the inside parts removed from the 4 oranges.
Put the squeezed orange juice, water and the sugar in a small pan, mix them together and heat it up.
Remove the pan from the heat before boiling, add the soaked gelatin, mix well until incorporated.
Add the lemon juice, let it cool over a bowl with ice.
When it gets cold and has thickened a little, pour it into the prepared orange cups.
Chill for 1 hour in the fridge.
Arrange the orange pieces as decoration.