Heat a large skillet over medium-high heat and cook sausage, breaking apart with a spatula, until fully cooked and no longer pink. Drain as much grease as possible from the skillet, using paper towels if necessary. Set aside to cool for 10-15 minutes before proceeding with the next step.
Preheat oven to 350℉. Spray a 2 1/2 quart (I used an 11-inch oval) baking dish with nonstick cooking spray and set aside.
In a medium-sized bowl, combine Italian sausage, softened cream cheese, 3/4 cup shredded Mozzarella, Parmesan cheese, diced tomatoes, Pepperoncinis, Italian seasoning, garlic powder and red pepper flakes.
Spread the sausage mixture into the prepared baking dish. Sprinkle with reserved 3/4 cup mozzarella and a sprinkle of Italian seasoning if desired.
Bake at 350℉ for 20 minutes, or until bubbly. For additional browning of the cheese, switch to the broiler during the last few minutes, but watch closely as it can burn quickly.
Garnish with fresh chopped basil, if desired. Serve with crostini or crackers for dipping.
Notes
It is very important to drain the grease from the sausage. Use paper towels to blot the meat if necessary. If there is a lot of grease left behind it will just make the dip greasy.