Season shrimp with salt and pepper. Heat 1 tablespoon olive oil in a large nonstick skillet over medium heat; add shrimp and fennel seeds to pan. Cook until shrimp are opaque, turning often (about 3 minutes). Remove pan from heat; toss shrimp with 1 tablespoon lemon juice.
In a large bowl, combine watercress, fennel, radishes, remaining olive oil, and remaining lemon juice, tossing well.
Divide salad among 4 plates; top each evenly with shrimp, mint, and cheese.
