Transfer 1 1/2 cups of the walnuts to a food processor. Add the oil and lime juice and pulse until the walnuts are coarsely chopped. Transfer to a bowl and season with salt and pepper. Add the beets, apple, avocado, fennel and Manchego and toss. Add the mesclun and tortilla chips, season with salt and pepper and toss again. Transfer the salad to plates, garnish with the remaining walnuts and serve right away.