Heat small skillet over medium heat. Add cumin seeds and toast until aromatic and slightly darker, about 2 minutes. Cool; grind finely in spice mill. Whisk lime juice, honey, and cumin in small bowl. Gradually whisk in oil; stir in dill. Season dressing with salt and pepper. DO AHEAD:Can be made 1 day ahead. Cover and chill. Bring to room temperature.
Cook peas in pot of boiling salted water until almost tender, about 5 minutes for fresh (or about 2 minutes for frozen). Drain; rinse under cold water, then drain well. Transfer to large bowl. Add radishes, feta, and dressing; toss. Season with salt and pepper. If using pea tendrils or sprouts, divide among bowls. Divide salad among bowls. Serve.