Gently stir together crabmeat, breadcrumbs, scallions, eggs, lemon zest, 1/2 cup of the mayonnaise, 1/4 cup of the parsley, 1 1/4 teaspoons of the salt, and 1/2 teaspoon of the pepper in a medium bowl. (Do not break up the larger pieces of crabmeat.) Shape mixture into 12 (3-inch-wide) patties (about 1/2 cup per patty). Place patties on a baking sheet lined with aluminum foil; cover and chill 15 minutes.
Meanwhile, separate fennel stalks from bulb. Pick fronds from stalks; discard stalks. Chop fronds to equal 3 tablespoons. Trim top and bottom of fennel bulb; discard ends. Thinly slice fennel bulb to equal about 2 cups.
Combine sliced fennel bulb, chopped fennel fronds, angel hair coleslaw, thinly sliced radishes, and remaining 1/4 cup parsley in a medium bowl. Stir together chopped capers, caper brine, honey, lemon juice, and remaining 1/2 cup mayonnaise, 3/4 teaspoon salt, and 1/2 teaspoon pepper in a small bowl. Pour caper mixture over fennel mixture; toss to coat.
Heat 3 tablespoons of the oil in a large nonstick skillet over medium-high. Place 6 of the crab cakes in skillet; cook until golden brown, 3 to 4 minutes per side. Repeat with remaining 3 tablespoons oil and 6 crab cakes. Serve crab cakes with slaw and lemon wedges.