In a blender, puree the orange juice concentrate, vanilla, sugar and coconut milk until very smooth.
At this point, taste the mixture and adjust sugar/orange juice concentrate to your personal preference. If adding more, puree once more to be sure it's completely smooth.
Pour into the bowl of an ice cream machine that has been in the freezer overnight.
Process according to manufacturer's instructions, or until soft-serve consistency has been reached. At this point, add in the pineapple and orange pieces. Fold to combine.
Spoon this mixture into a loaf pan and freeze until it firms up. I leave mine for several hours before scooping. Of course, you can always enjoy it as soft-serve as well.