Preheat oven to 450°F (232°C) and position the rack in the upper third.

In a medium bowl, combine olive oil, kosher salt, white wine vinegar, and freshly ground black pepper.

Whisk the ingredients together until well combined.

Add halved red seedless grapes, coarsely chopped mint leaves, and finely chopped red onion to the bowl.

Stir to coat all ingredients with the dressing.

Set the grape-mint relish aside.

Place lamb sausages on a baking sheet.

Roast in the preheated oven for approximately 15 minutes, or until fully cooked and browned, and a meat thermometer registers 160°F (71°C).

Serve the roasted lamb sausages immediately with the grape-mint relish.