Grilled Meatball Sandwich

Name: Grilled Meatball Sandwich
Ingredients: 2 lb (1 kg) ground beef; 1/2 cup (4 oz/125 g) ricotta cheese; 1/4 cup (1 oz/ 30 g) freshly grated Parmesan cheese; 1/4 cup (1/3 oz/10 g) Panko bread crumbs; 4 large eggs, lightly beaten; 2 Tbsp minced fresh flat-leaf parsley; 1 garlic clove, minced; 1 tsp red pepper flakes; Kosher salt; Oil for grill; 1 large baguette; 8 oz (250 g) thinly sliced Provolone cheese; Arugula Pesto