In a large saute pan, add the sausage and cook over medium-high heat until browned and cooked through, about 7-8 minutes. Remove the sausage with a slotted spoon and transfer to a paper towel-lined plate to get rid of any excess grease.
Grease a 9x13 inch baking dish with butter or a non-stick spray. Add the torn bagel pieces and sausage to the dish. Dollop teaspoons of mascarpone cheese on top and sprinkle on the mozzarella and cheddar cheese. Set aside.
In a large bowl, whisk together the eggs, half and half, milk, dry mustard, garlic powder, onion powder, poppy seeds, cayenne pepper, salt, and black pepper until thoroughly combined. Pour the mixture over top of the casserole. Cover and refrigerate for at least 4 hours or overnight.
When you are ready to bake, preheat your oven to 375 degrees F and bake the strata, covered, for 35-40 minutes. Remove the cover, and bake for an additional 10-15 minutes or until the top begins to brown. Remove from oven and let stand for 5-10 minutes before serving.
Top with fresh greens and sliced green onions. Enjoy!