Prepare the mussels: Open bag of mussels into a colander. Rinse with cold water. Inspect mussels and remove any 'beards'. Discard any open mussels or mussels with broken shells.
In a large saute skillet heat olive oil over medium to medium-high heat. Add pancetta and cook until fat is rendered and pancetta is lightly browned.
Add sliced garlic and cooking, stirring or sautéing until just browned, about 2 minutes. Add shallots and cook for 1 minute.
Carefully add mussels to the pan and immediately deglaze the pan with the white wine. Stir with a wooden spoon or spatula, making sure to scrape the bottom of the pan.
Add tomatoes, salt, and red pepper flakes. Stir to combine. Let the heat from the sauce steam the mussels open while the sauce reduces, about 5 to 7 minutes. Stir occasionally.
Best if served right away. Especially with crusty bread for dipping.
Notes
Pancetta can be left out for a pescatarian version. If leaving out, add ½ tablespoon of butter to the final sauce for a little fat to cut the acidity of the tomatoes.