Cook the Book: Pesto Beef Burger

Name: Cook the Book: Pesto Beef Burger
Ingredients: 2 pounds coarsely ground chuck, chilled; Cilantro-Arugula Pesto (recipe below); Freshly ground black pepper; 2 tablespoons olive oil; Sea salt; 4 thick slices (about 6 ounces) provolone cheese; 4 ciabatta buns; Grilled Onion Steaks (recipe below); 1 large tomato, cut into 4 thick slices; Large handful arugula; Fleur de sel (optional; 1 large bunch fresh cilantro; 12 roasted, salted macadamia nuts; 1 or 2 garlic cloves, to your taste; 2 cups packed arugula; 1 teaspoon freshly squeezed lime juice; 1/3 teaspoon freshly grated lime zest; 6 tablespoons extra-virgin olive oil; 1/4 cup freshly grated Pecorino Romano cheese; Sea salt and freshly ground black pepper; 2 tablespoons olive oil, plus more for brushing; 2 tablespoons Dijon mustard; 2 tablespoons honey; 1 tablespoon balsamic vinegar; 2 large (about 10 ounces each) sweet onions, such as Vidalia or Maui; 8 to 12 soaked bamboo skewers