Grilled Bread with Chimichurri

Name: Grilled Bread with Chimichurri
Ingredients: 1/2 cup plus 2 tablespoons olive oil; 1 medium onion, thinly sliced; 1/2 cup packed fresh flat-leaf parsley leaves; 1/2 teaspoon coarse salt; 2 tablespoons red-wine vinegar; 2 tablespoons packed fresh cilantro leaves; 1 tablespoon fresh oregano leaves; 1 tablespoon fresh lemon juice; 2 garlic cloves, finely chopped; 1/4 teaspoon freshly ground pepper; 1/2 teaspoon ground cumin; 1/8 teaspoon cayenne pepper; 1 loaf ciabatta, halved horizontally