In a large saucepan, combine half of the fennel with the leek, garlic, fennel seeds, coriander seeds, black peppercorns, orange zest, orange juice, white wine, water, and 2 teaspoons of kosher salt and bring to a boil. Simmer over low heat for 20 minutes. Let cool for 15 minutes.

Add the shrimp to the saucepan and cook over low heat until pink and curled, about 5 minutes. Remove from the heat and let the shrimp marinate in the warm liquid for 15 minutes. Using a slotted spoon, transfer the shrimp to a plate. Halve each shrimp lengthwise and refrigerate until cool. Strain the poaching liquid, reserving 1 cup.

In a small saucepan, boil the reserved poaching liquid over high heat until reduced to 2 tablespoons, 15 minutes; transfer to a large bowl and whisk in the oil and vinegar. Season with salt and piment d'Espelette. Add the cantaloupe, honeydew, frisee, tarragon, shrimp, and the remaining sliced raw fennel. Season the salad with salt and piment d'Espelette, toss gently and serve.

The poached shrimp and dressing can be prepared up to 1 day ahead; refrigerate separately.

Piment d'Espelette is a spicy ground red pepper from the Basque region of France. It's available at specialty food stores.