In a skillet, heat 1 tablespoon of extra virgin olive oil over medium heat. Add the sliced onions and sauté for about 5–7 minutes until they're soft and translucent. Transfer the onions to a bowl to cool while preheating your oven.

Set your oven to 180°C (360°F) to preheat it.

Wash and slice fresh tomatoes thinly or drain canned tomatoes and blot excess moisture with paper towels.

Unroll the vegan puff pastry onto a tart pan or baking sheet lined with parchment paper. Pierce the pastry with a fork and spread a layer of Dijon mustard over the base.

Layer the sautéed onions over the mustard, sprinkle with salt and herbes de Provence, then add the sliced tomatoes and thin garlic slices.

Add remaining fresh herbs over the tomatoes and drizzle with olive oil. Fold the edges of the pastry slightly to contain the filling.

Bake in the preheated oven for about 40 minutes until the pastry is golden brown. Let cool for 10 minutes before slicing.