Preheat the electric smoker to 250°F. Add the wood chips according to the manufacturer’s instructions.

In a large mixing bowl, combine the ground beef, Italian sausage, breadcrumbs, egg, Parmesan, garlic, Italian seasoning, salt, and black pepper. Mix gently until just combined, taking care not to compact the meat.

Lay a sheet of parchment paper on a clean work surface. Shape the meat mixture into a rectangle about ½ inch thick. Arrange the spinach down the center, leaving a border around the edges, then place the mozzarella strips over the spinach.

Use the parchment to lift one long side of the meat mixture over the filling. Fold the other side over to seal, then pinch the ends and seam closed. Shape the loaf evenly so the filling is enclosed.

Transfer the meatloaf to a smoker-safe pan or rack, seam side down. Spoon ¼ cup of marinara over the top.

Smoke until the center reaches 160°F on an instant-read thermometer, checking the thickest part of the meat without touching the filling. During the last 15 minutes, spread the remaining marinara over the top.

Remove the meatloaf from the smoker and let it rest for 10 minutes before slicing. This helps the melted mozzarella stay inside the slices.