Step 1

In a large skillet, heat 3 tablespoons oil over medium-high heat until shimmering. Add mushrooms and cook, stirring, until tender and their water has evaporated, about 5 minutes. Add leek, garlic, and thyme, season with salt and pepper, and cook until leak is tender, about 4 minutes. Transfer to large bowl and stir in 1/4 cup cider vinegar. Let stand 15 minutes.

Step 2

In a large bowl, stir together spelt, cucumbers, and mushroom-leek mixture. Stir in remaining 6 tablespoons olive oil, 2 tablespoons cider vinegar, parley, and chives, and season with salt and pepper. Spoon salad into bowls and sprinkle with espelette pepper, if using.