In a 12-inch skillet, heat the oil over medium-low. Add the sausages, cover, and cook, turning once, until opaque and half-cooked, about 8 to 10 minutes. Remove the lid, increase the heat to medium-high, and cook sausages, turning as needed, until browned all over and almost cooked through, about 8 to 10 minutes.
Add the grapes, chili flakes, and garlic, season with salt and pepper, and cook, covered, until the grapes begin to burst, 3 to 4 minutes. Remove the lid, and cook, stirring, until the grapes break down slightly but are still holding their shape, about 2 minutes more. Remove from the heat, and serve two sausages per person with lots of grapes spooned over top.