Adjust racks to top and middle positions and preheat oven to 425 degrees. Wash and dry produce.

Trim and discard root end from lettuce; separate leaves and tear into bite-size pieces over a large bowl.

Grate Parmesan over a small bowl. 

In a second large bowl, combine chicken*, panko, mayonnaise, Italian Seasoning, half the Parmesan, salt (we used ½ tsp; 1 tsp for 4 servings), and pepper.

Form into 8-10 1-inch meatballs (16-20 meatballs for 4).

Heat 2 TBSP oil in a large, preferably ovenproof, pan over medium heat. Add 5 meatballs and cook until browned on all sides, 30-45 seconds per side (they’ll finish cooking in next step).

Transfer seared meatballs to a plate; repeat with remaining meatballs. Turn off heat; wipe out pan.

Add marinara to pan used for meatballs (if your pan isn’t ovenproof, use an 8-by-8-inch baking dish instead).

Arrange meatballs in pan, nestling each one in sauce. Bake on top rack until meatballs are cooked through, 6-8 minutes.

Remove from oven; carefully sprinkle meatballs and sauce with mozzarella. Return to top rack and bake until cheese melts, 2-3 minutes more.

While meatballs bake, halve ciabatta and place on a baking sheet. Drizzle cut sides with olive oil and sprinkle with remaining Parmesan. Toast on middle rack until cheese melts.