Bring a large pot of salted water to a boil. Place the radishes in the pot and cook for 12 to 15 minutes until fork tender. Drain them in a colander and transfer to the fridge to let cool.
While the radishes are cooling, prepare the other ingredients. Whisk together the Greek yogurt, mustard, lemon juice, and salt in a small bowl.
Combine the radishes, celery, onion, eggs, and dill in a large bowl. Pour the dressing on top and mix until coated. Taste and add more salt, pepper, and dill as desired. Serve immediately or, if the radishes are still a little warm, let the dish cool in the fridge for a little while longer.
This dish is best served right away but can be stored in the fridge for a couple of days.
For a variety of colors, use Easter egg radishes if you can find them.
Cook the eggs in advance or in a separate pot while the radishes are cooking.