DO-AHEAD TIP: Cook and crumble sausage.
Preheat grill to MEDIUM-LOW. Melt the ghee (or coconut oil) in a large all-metal skillet over medium-high heat.
Add onion, mushrooms and sweet potato; cook until softened. Add cooked sausage.
Pour beaten eggs over the top then sprinkle with chopped cilantro, salt and pepper.
Transfer skillet to the grill; close the lid and grill for 10 to 12 minutes or until frittata is set and no longer runny.
Remove from heat and serve.