1. Cook the quinoa in 2 and a half times its volume of salted water, until the small white germ appears.
2. Melt the onion in slices in olive oil.
3. When it starts to melt, add the zucchinis and thyme.
4. Cook over medium heat for 10 minutes, then add the sliced mushrooms, and cook for another 5 minutes, season with salt and pepper.
5. Mix the cooked quinoa with the vegetables, add 2 beaten eggs and the heavy cream.
6. Pour everything into a buttered gratin dish, and bake in the oven at 200°C (392°F) for about 40 minutes (until the top is golden brown).