Spray 13x9-inch (3-quart) glass baking dish or 3-quart casserole with cooking spray.
In large bowl, toss potatoes and 1 tablespoon of the taco seasoning mix until evenly coated.
Pat in baking dish.
Spray 10-inch skillet with cooking spray.
Add the sausage and onion; cook over medium-high heat 5 to 7 minutes, stirring occasionally, until sausage is no longer pink.
Drain.
In same large bowl, beat eggs, cheese, milk, salt, pepper and remaining taco seasoning mix with whisk until well blended.
Stir in sausage mixture and salsa.
Carefully pour over potatoes in baking dish.
Bake uncovered about 40 minutes or until eggs are set in center.
Let stand 10 minutes before serving.
Notes & Wine Advice
Make-Ahead Magic
You can assemble the Mexican Breakfast Casserole, right, as directed the night before; cover and refrigerate. In the morning, simply uncover and pop it in the oven. You may need to add an extra 5 to 10 minutes to the bake time.