Preheat oven to 350 F.
Combine bulgur and boiling water in a bowl. Let stand for 15 minutes.
In a skillet, heat oil. Add onion and garlic. Saute until golden brown.
Add spinach and saute until leaves wilt. Turn off heat.
Add mint, Parmesan and 1/4 teaspoon salt. Stir to combine.
Add bulgur and stir to combine.
Cut off ends of zucchini and cut vertically down the middle. Scoop out the middle. Sprinkle insides with a little salt and pepper.
Stuff insides with bulgur spinach filling. Sprinkle grated Gruyere on top.
Place in a greased baking dish. Bake for 30 minutes.