For the sausage: If raw, cook in a 400°F oven to an internal temperature of 160°F using a thermometer. If already cooked: Place in a 400 degree oven until warmed through or slice and brown in a nonstick pan on medium heat.
Preheat the oven broiler on low.
Heat a large oven-safe nonstick or cast-iron skillet over medium heat. Once hot, add in the oil and leeks. Saute until they start to brown, then add in the tomatoes, garlic, and mushrooms. Continue to saute until the mushrooms soften. Season with salt and pepper.
Pour the eggs into the pan. Stir the eggs around to distribute the ingredients evenly. Evenly distribute the basil and goat cheese. Place the skillet under the broiler until the eggs are firm in the middle and slightly browned on top, about 6-10 minutes. Let sit for 3 minutes.
To release the frittata from the pan, run a spatula around the edge, then underneath, until you can slide or lift it out onto a cutting board or serving plate.
Cut into wedges and serve with toast, sausage, and grapes.