Heat a small saucepan over medium heat.

Once it is hot, add the chilies and toast for about 2 minutes, or until just aromatic, being careful not to burn them.

Add the plums, onions, water, vinegar, lime juice and garlic and bring to a simmer.

Reduce the heat to medium-low and cook until the mixture thickens, about 10 to 15 minutes.

Pour the mixture into a blender, and process until no large chunks remain.

Strain the mixture through a chinois or fine mesh strainer.

Serve the sauce warm.