Slice the top off the orange about one-third of the way down, using a sharp knife, and reserve. Suspend the orange parts over a mixing bowl and scoop out as much flesh as possible, allowing the juices to run into the bowl. Reserve the juice and the orange skin.
Place the chopped strawberries into the orange skin. Pour over the reserved orange juice, adding a little cold water to top up as necessary.
Place the top part of the orange back onto the bottom part. Carefully transfer the orange to a freezeable, lidded container (propping it up as necessary with scrunched up aluminium foil). Freeze for at least two hours, or until the filling has frozen.
To serve, remove the top of the orange from the orange and eat the contents with a teaspoon.