Preheat the oven to 375.
Heat a drizzle of the olive oil over medium heat. Add the sliced onions and sauté until wilted, for about 5 minutes. When they start to stick and get a bit of color, pour in a splash of water to help them become more tender.
Add the sliced mushrooms and cook until they are softened. Sprinkle with half of the thyme, half of the garlic, and half of the salt.
Meanwhile, toss the remaining thyme, garlic and salt with the almond meal, grated parmesan cheese and butter or olive oil. Fold about a tablespoon of this mixture with the mushrooms.
Spread the mushrooms in the tart pan. Spoon dollops of the cream cheese (goat cheese, mascarpone or ricotta) every 2 inches or so apart.
Clump the almond-cheese crumble in your hand and then break pieces off all over the tart. Sprinkle the top with fresh black pepper all over.
Bake for 15-20 minutes until the top is golden.
Alternatively, you could chill it prior to baking and store for later. When you are ready to eat it, just add an extra 10-15 minutes of bake time.