How to Make It
Preheat oven to 350°F. Lightly grease a 13- x 9-inch broiler-safe baking dish with cooking spray, and set aside. Heat oil in a large skillet over medium-high. Add sausage; and cook, stirring to break up sausage, until browned and just cooked through, about 7 minutes. Transfer to a plate lined with paper towels. Do not wipe skillet clean.
Add bell peppers, scallions, and 3/4 teaspoon of the salt to skillet. Reduce heat to medium, and cook, stirring occasionally, until tender-crisp, 6 to 8 minutes. Remove from heat.
Toss together potatoes and flour in a large bowl. Stir in cheese, cooked sausage, and bell pepper mixture. Spoon into prepared baking dish.
Whisk together eggs, milk, and remaining 1 teaspoon salt in a large bowl until thoroughly blended. Pour evenly over potato mixture. Bake, uncovered, in preheated oven until eggs are set in middle, about 55 minutes. Increase oven temperature to broil. Broil until top of casserole is browned in spots, 2 to 3 minutes. Remove from oven; let stand 15 minutes before serving.