Martha and Sean Rembold of Brooklyn's Marlow and Sons share Sean's recipe for a muffaletta panini.
Preheat a panini press to high heat. Spread olive salad over cut sides of bread.
On one half of each piece of focaccia, layer 2 ounces mortadella, 1 1/4 ounces soppressata, 1 ounce salami, 1 ounce coppa, and 2 ounces cheese. Sandwich second half of bread over meats and cheeses and transfer to panini press. Press until heated through, 4 to 5 minutes.
Meanwhile, place arugula in a medium bowl. Drizzle with olive oil and lemon juice; season with salt and toss to combine.
Remove sandwiches from press and cut each in half. Serve immediately with arugula.