While the dough rests in the fridge, you can prepare the veggies. Heat a little bit of vegetable oil in a saucepan, add the onion and fry over medium heat for about 1 minute. Add garlic, pepper, leek, spinach, and a pinch of salt. Sauté for a few minutes until all the water evaporates. Let cool. If there is still water left, then squeeze it out as much as possible.