Preheat your oven to 375°F (190°C) and prepare a 9-inch pie plate by spraying it with cooking spray. Fit the pie crust into the plate.

In a large skillet, heat 2 tablespoons of avocado oil over medium-high heat. Add crumbled breakfast sausage, cooking for 5-7 minutes until browned.

In the same skillet, add 2 tablespoons of unsalted butter over medium heat. Once melted, add diced yellow onion and sauté for 15-20 minutes until caramelized. Add diced red and green bell peppers, cooking for an additional 4-5 minutes.

Add minced garlic to the pan and cook for 1-2 minutes until fragrant. Season with dried sage, kosher salt, and freshly ground black pepper.

In a large mixing bowl, whisk together 4 large eggs, 1 cup of whole milk, and 1/2 cup of heavy cream until smooth. Fold in the cooked sausage and sautéed vegetable mixture along with 1 cup of sharp cheddar cheese.

Pour the filling into the prepared pie crust and spread evenly. Bake for 45-55 minutes until the top is golden brown and the center has a slight jiggle.

Let the quiche cool for about 10 minutes before slicing. Serve warm or at room temperature.