Goat Cheese and Red Onion Frittata Sandwich Crunchified with Pepper Relish

Name: Goat Cheese and Red Onion Frittata Sandwich Crunchified with Pepper Relish
Ingredients: Eight 1/4-inch slices pancetta; Kosher salt and freshly ground black pepper; 2 tablespoons olive oil; 1 medium red onion, halved and thinly sliced; 1 clove garlic, finely chopped; 8 large eggs; 4 ounces goat cheese, cut into small pieces; 2 tablespoons chopped fresh herbs, such as parsley or basil; 2 tablespoons hot pepper relish, such as B&G; 4 ciabatta rolls, halved horizontally and lightly toasted; 4 ounces baby arugula or watercress