Place mussels in a colander and rinse well, discard any mussels that are open.
Heat oil in a large deep cast iron skillet or deep sauce pot over medium heat.
Add onions and garlic and sauté 1-2 minutes until soft and translucent.
Add in oregano and chillies and sauté for an additional 30 seconds stirring.
Pour in ouzo or wine and stir.
Add in canned tomatoes and fill the can with 1/3 cup water. Stir to get all the tomato out of the can and pour into the pot.
Season with salt and pepper.
Reduce heat to simmer and let sauce cook for 10 minutes for all the flavours to absorb.
Stir in dill and turn heat up to medium. Add in mussels, stir well to mix and cover with lid.
Cook mussels covered for 6–8 minutes or until all mussels have opened.
Garnish with green onions and dill. Serve immediately with crusty bread for mopping up the sauce.