Preheat oven to 425 degrees F.
Unroll pie crust and press into a pie plate. Prick the bottom and sides of the pie crust with a fork.
Bake the pie crust for 10 minutes. Lower oven temperature to 325 degrees.
Cook sausage over medium-high heat, until cooked through and crumbled. Set aside.
Add olive oil to a medium skillet and add onions and garlic, cook 2 minutes.
Add spinach and cook for 5 minutes, stirring often.
Add eggs to a large bowl, add milk and salt and whisk until well combined. Add shredded cheese, sausage and spinach mixture. Stir until well combined.
Pour into pie shell and bake for 50-55 minutes or until center is set.
Remove from oven and allow to rest 10 minutes before slicing.