How to Make It
Preheat the oven to 350°. Light a grill. Put the walnuts in a pie plate and toast in the oven for 7 minutes, or until they are golden brown. Transfer the walnuts to a plate and let cool, then coarsely chop.
In a medium bowl, toss the peaches with 1/2 tablespoon of the olive oil and season with salt and pepper. Grill the peaches over a medium-high fire until softened and lightly browned, about 5 minutes per side. Transfer the peaches to a work surface and cut each half in half.
In a medium bowl, mix the vinegar with the remaining 2 tablespoons of olive oil and season with salt and pepper. Add the arugula and frisée and toss well. Transfer the salad to a platter and scatter the Cabrales and toasted walnuts on top. Arrange the peaches around the salad and serve.