Bring 6 cups water to boil; add shrimp, and cook 3 to 5 minutes or until shrimp turn pink.
Peel shrimp, and devein, if desired.
Bake walnuts in a shallow baking pan at 350° for 7 minutes or until toasted. Set aside.
Rinse fennel thoroughly. Trim and discard bulb base. Remove and discard outside stalks. Chop 2 tablespoons of stalk, and reserve. Cut bulb crosswise into thin slices.
Process lemon juice and next 4 ingredients in a blender until smooth. Turn blender on high; gradually add oil in steady stream.
Combine shrimp, walnuts, sliced fennel, lettuce, avocado, and carrot. Add vinaigrette, and toss gently. Sprinkle with reserved chopped fennel.
Note: Boston and Bibb are butter lettuces.
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