Preheat the oven to 375°F/180°C and line a baking pan with baking paper.
Cut the zucchini in half lengthwise. Scoop out the flesh using a spoon and place the zucchini halves on the prepared baking pan.
Finely chop the remaining zucchini flesh and heat the oil in a frying pan. Add the zucchini flesh and the salmon and sauté for 3-5 minutes, seasoning with salt and pepper. Flake the salmon with a fork while it’s cooking in the pan and add the garlic.
Stir in the marinara sauce and mix well.
Spoon the mixture into the zucchini halves and top with a generous layer of mozzarella cheese.
Bake in the preheated oven for about 20 minutes until the zucchini is cooked through and the cheese is golden and bubbly. Serve hot.