Preheat a smoker to 250°F. Line a small rimmed baking sheet with foil, then set a wire rack on top.
In a large bowl, combine the ground beef, egg, Parmesan, almond flour, onion, garlic, parsley, Italian seasoning, salt, black pepper, and 2 tablespoons of the marinara. Mix gently just until combined.
Shape the mixture into a compact loaf about 8 inches long. Place it on the wire rack, leaving space around the sides so the smoke can circulate.
Smoke the meatloaf until its center reaches 155°F, about 1 1/2 to 2 hours depending on its shape and the smoker. Use an instant-read thermometer to check the temperature.
Spread the remaining marinara over the top. Continue smoking until the center reaches 160°F.
Remove the meatloaf from the smoker and let it rest for 10 minutes before slicing. This helps the slices hold together.