Step 1 Heat a grill over medium-high heat until hot.
Step 2 Meanwhile, heat a large saute pan over medium heat. Add the olive oil, shallots, garlic and chorizo and cook, stirring frequently, until the shallots are softened, 4 minutes. Stir in the red wine and reduce it by half, 3 to 5 minutes. Remove from heat.
Step 3Place the mussels in a wire basket and place over the grill just until they begin to open.
Step 4Transfer the mussels to the saute pan and toss with chorizo and reduced wine. Heat the pan over high heat until it begins to boil. Stir in the tomatoes, parsley and butter, and season with a pinch of salt and several grinds of pepper, or to taste.
Step 5Remove from heat and serve immediately.