Preheat oven to 425°F.
Add potatoes to a bowl with 1 tbsp of oil and season with salt and pepper;
Coat potatoes and then place on a prepared baking sheet.
Roast potatoes 10 minutes.
While potatoes roast, combine red onion and vinegar in a bowl.
Season red onion & vinegar with salt and pepper. Set aside.
After 10 minutes of roasting, add the quartered radishes to the potatoes and roast until potatoes are golden brown and radishes are tender, additional 15 minutes or so.
While the potatoes & radishes cook, Season lamb with salt and pepper.
Heat 1 tbsp oil in a large skillet over medium-high heat.
Cook lamb to desired degree of doneness, 3 to 5 minutes per side for medium- rare; transfer to a platter.
Steam broccoli for about five minutes, while lamb is cooking.
Add mint, feta, and remaining 2 tbsp oil to red onion/vinegar mixture.
Remove broccoli from the steamer
Serve lamb topped with relish and vegetables alongside.