Photograph by Anna Williams
Heat oven to 350 degrees. Spread pecans on a baking pan. Bake until golden and fragrant, 10 to 15 minutes. Cool on a wire rack. Halve pecans; set aside.
Slice fennel bulb very thin using a mandoline or a sharp knife. Transfer to a large bowl; add 1 teaspoon lemon juice, and toss.
Cut apple, with skin on, into thin wedges; add to fennel, and toss to combine. Add grapes, celery, escarole, and half the dill to bowl. Toss to combine. Salad may be made to this point up to 4 hours ahead.
In a small bowl, combine remaining 2 tablespoons lemon juice, yogurt, olive oil, and salt and pepper to taste. Drizzle vinaigrette over the salad, using only as much as needed to lightly coat the salad. Transfer to a serving bowl; garnish with remaining dill and the pecans. Serve immediately.