Mussels have three things going for them: They’re tasty, quick to cook, and delicious. Using clean farmed mussels negates their one big drawback—the tedious chore of scrubbing and debearding.
In a large pot, heat the oil over moderately low heat. Add the onion and garlic and cook, stirring occasionally, until the onion is translucent, about 5 minutes. Stir in the parsley, tomatoes, thyme, and red-pepper flakes. Reduce the heat and simmer, partially covered, for 15 minutes, stirring occasionally.