Source: Tourism PEI
Rinse the fresh blue mussels in tap water.
In saucepan, bring water or wine to boil.
Add fresh blue mussels, cover and steam over high heat until open (5-8 minutes). Remove from heat, reserving 2 tbsp of cooking liquid. Remove mussel meat from shells, reserving half shells.
In a bowl, combine reserved liquid, oil, lemon juice, garlic, parsley mixture and tomatoes; add fresh blue mussels and stir gently.
Cover and refrigerate for 3 hours.
To serve, place a mussel in each half shell and cover with tomato mixture. Arrange on platter.