Place the cherries and sugar in a medium saucepan and cook over a high heat until the cherries have completely thawed and syrup starts to form, stirring often (for about 5 minutes). Puree the mixture and pour back into the saucepan.
Add the quinoa, coconut milk and water, stir thoroughly, cover and bring to a boil. Lower the heat to a low simmer and cook for 35-40 minutes, until the quinoa has softened and thickened, stirring every few minutes (ensure the mixture doesn't stick to the pan). If the mixture starts to bubble up too much open the lid a little.
Serve hot or cold with crushed pistachios or simply on its own. The pudding will thicken as it stands (you can add a bit more coconut milk, or any other milk or water).