Green Bean Salad with Fennel and Toasted Pecan Dukkah

Preheat oven to 325ºF. Spread pecans on a rimmed baking sheet. Toast, tossing once, until fragrant and lightly golden, 8–10 minutes. Let cool completely.
Meanwhile, toast sesame seeds in a medium skillet over medium-low heat, stirring frequently, until fragrant and lightly golden, about 5 minutes. Add coriander, cumin, and fennel seeds and toast, stirring frequently, until sesame seeds are golden and spices are fragrant, about 2 minutes more. Transfer to a plate and let cool completely.
Coarsely chop 1/4 cup pecans; set aside. Pulse sesame seed mixture, 1/2 tsp. salt, 1/2 tsp. pepper, and 1/2 cup pecans in a food processor until coarse, dry, and crumbly; do not let it become a paste.
Cook green beans in a large pot of boiling salted water until crisp-tender, 5–7 minutes. Drain, then transfer immediately to a large bowl filled with ice water. Drain again and pat dry.
Meanwhile, coarsely chop fennel fronds; set aside. Cut fennel bulb in half lengthwise, then thinly slice each half lengthwise.
Whisk lemon zest, oil, 1/2 tsp. salt, and 1/4 tsp. pepper in a large bowl. Add green beans, fennel bulb, and half of the dukkah and toss to combine. Season with salt and pepper. Transfer salad to a serving platter, then top with fennel fronds, remaining dukkah, and remaining 1/4 cup pecans.
Dukkah can be made up to 3 days ahead; store in an airtight container at room temperature.