How to Make It
Whisk vinegar, mustard, salt, and pepper. Whisk in oil.
Place eggs in a medium saucepan and add enough water to cover; bring to a boil. Remove from heat and cover. Let stand for 7 minutes. Transfer to a large bowl of ice water to cool.
Peel eggs and slice. Gently toss eggs, capers, parsley, and radicchio with vinaigrette. Divide among toasts and serve immediately.