Cook sausage in large skillet over medium-high heat, breaking into small pieces. Add onion. Cook until sausage is completely cooked through. Drain any fat.
Generously spray 13 x 9-inch baking dish with cooking spray. Add bread cubes. Top with cooked sausage.
Add bacon to same skillet and cook until crispy. Drain well. Add to baking dish.
Whisk together eggs and milk in a large bowl. Stir in mustard, salt and pepper and whisk until well blended. Evenly pour over bread and sausage mixture. Cover and refrigerate at least 8 hours or overnight.
If using a ceramic or glass baking dish, place dish in a COLD oven and bake at 350°F for 50 to 60 minutes or until knife inserted in center comes out cleaning. If using a metalic baking dish, preheat oven to 350°F and bake for 40 to 45 minutes. Remove foil halfway through baking.
Sprinkle with cheese last 10 minutes of baking.
Let strata stand for 10 minutes before serving.
* Almost any plain or savory loaf or dinner roll will work in this recipe. You'll need about a 1/2 loaf. Only have a slice or two? Freeze stale bread and when you've got 7 to 9 slices you'll have enough to make this delicious strata.