Just a little shrimp goes a long way in these spring-inspired cakes. If using frozen shrimp, make sure to thaw completely before peeling and chopping; otherwise the shrimp will fall apart. You can use fresh basil instead of tarragon.
Combine snap peas, onion, 1 tablespoon oil, vinegar, 1/2 teaspoon salt, and 1/4 teaspoon pepper in a bowl. Let stand 10 minutes.
Shred zucchini on the large holes of a box grater. Place shredded zucchini on a clean kitchen towel; squeeze well to remove excess liquid. Combine zucchini, remaining 1/4 teaspoon salt, remaining 1/4 teaspoon pepper, panko, tarragon, shrimp, and egg in a bowl.
Heat remaining 2 tablespoons oil in a large nonstick skillet over medium-high. Spoon 1/4 cup zucchini mixture loosely into a dry measuring cup. Add mixture to pan; flatten slightly. Repeat procedure 7 times to form 8 cakes. Cook 3 minutes on each side or until golden brown. Serve cakes with snap pea mixture.