Heat small skillet over medium heat. Add the fennel seeds and toast until aromatic, about 2 minutes. Cool the toasted fennel seeds and grind them finely in a spice mill. Whisk lime juice, honey, and ground fennel in a small bowl. Whisk in oil and stir in fresh fennel. Season the dressing with kosher salt. Blanch the peas in a pot of boiling salted water until the peas are bright green, about 2 minutes. Plunge into ice water, and drain well. In a large bowl, combine the peas, radishes and dressing, and toss together. Lightly toss in the mizuna or pea shoots, and feta. Divide among 4 salad plates and serve.