Preheat Oven: Begin by preheating your oven to 350 degrees Fahrenheit.
Cook Sausage: In a large skillet, cook the sausage over medium-high heat. Make sure to break the meat into small crumbles as it cooks.
Add Vegetables: Once the sausage starts to brown, add the sliced banana peppers, chopped onions, and minced garlic to the skillet. Continue cooking until the sausage is fully cooked and no longer pink, and the peppers and onions have softened.
Prepare Cheese Mixture: While the sausage cooks, take a food processor and blend together the marinara sauce, cream cheese, ½ cup of mozzarella cheese, and all the parmesan cheese. Scrape down the sides of the processor as needed to ensure a smooth mixture.
Combine and Assemble: Remove the sausage and vegetables from heat. Stir in the cheese mixture until well combined. Transfer this mixture to a greased baking dish. Smooth the top and sprinkle the remaining 1 cup of mozzarella cheese evenly over the surface.
Bake: Place the baking dish in the preheated oven. Bake uncovered for 20-25 minutes, or until the dip is hot and bubbly, and the cheese on top has melted and turned golden.
Garnish and Serve: Optionally, garnish with extra sliced banana peppers. Serve the dip hot, accompanied by your choice of your favorite dippers like tortilla chips, pita chips, fresh veggies, or toasted bread for dipping.