Combine lemon zest, paprika, garlic, ¾ teaspoon salt and ¾ teaspoon pepper in a medium bowl. Add shrimp and toss to coat.
In a large pot, melt butter over medium-high heat. When butter is foaming, add shrimp and cook, stirring occasionally, until pink and starting to curl, 2 to 3 minutes. Using a slotted spoon, transfer shrimp to a plate; set aside.
Add leeks, season with salt and pepper, and cook over medium until leeks are soft and starting to brown on the edges, 4 to 5 minutes, stirring occasionally. Add beans and chicken broth and bring to a boil over high. Lower heat and simmer, 8 to 10 minutes. Stir in reserved shrimp and any juices from the plate, parsley and lemon juice, and season with salt and pepper. Serve with toasted bread.