Defrost green peas if using frozen. (Do not heat them in order to preserve freshness. I pour cold water over the peas and let them thaw this way.) Boil eggs and cool.
Combine peas, arugula, sliced radishes and cucumbers in a medium bowl.
In a mason jar combine the plain yogurt, mayonnaise, white wine vinegar, mustard, chopped dill, a pinch of salt and water, screw the lid on and shake vigorously until combined. You might want to add more water to a desired consistency. Alternatively, you can mix all dressing ingredients in a small bowl using a whisk.
Use 2-3 tbsp of Creamy Dill Dressing to dress your salad and reserve the rest for later use.
Sprinkle with feta and top with boiled eggs and avocado, cut into wedges. Serve immediately.