Heat a 10-inch cast-iron or other ovenproof skillet over medium-high heat.
Coat pan with cooking spray.
Remove sausage from casings and crumble into the pan.
Cook until browned, stirring to crumble, about 5 minutes.
Add cauliflower and ½ cup (118ml) water; cover, reduce heat to medium, and cook for 5 minutes.
Stir in marinara sauce and gnocchi; cover, reduce heat to medium-low, and cook until cauliflower and gnocchi are tender, about 6 minutes.
Preheat the broiler to high.
Uncover the pan, and sprinkle evenly with cheese.
Broil until the cheese melts, 1–2 minutes.
