Rinse the mussels under cold running water while scrubbing with a vegetable brush. Discard any with broken shells. Heat oil in a 6 to 8-quart stockpot. Saute the shallot, garlic and thyme to create a base flavor. Add the mussels and give them a good toss. Add wine, lemon juice, chicken broth and red pepper flakes; cover the pot and steam over medium-high for 5 minutes until the mussels open. Toss in the tomato, parsley and butter, recover the pot, and steam for another minute to soften. The tomatoes should keep their shape. Serve with plenty of grilled garlic bread to sop up the broth.