Preheat the oven to 450°F (232°C) and lightly grease a 9x13 inch baking dish with olive oil.
Run the bread slices briefly under water until just damp, squeeze out excess water, and crumble into small pieces.
In a large bowl, combine the ground spicy Italian chicken sausage, ground chicken, crumbled bread, eggs, grated Parmesan, grated shallots, grated garlic, chopped pepperoncinis, and a pinch of salt and pepper; mix until evenly combined.
Coat your hands with a little olive oil and roll the mixture into 2-tablespoon-sized meatballs. Place the meatballs evenly in the prepared baking dish.
Bake the meatballs uncovered for 15 minutes, until the outside is beginning to crisp but the centers are not fully cooked.
Remove the dish from the oven and pour the marinara sauce over the meatballs. Cover the dish with foil and return to the oven for 15 minutes, or until meatballs are cooked through.
Remove the foil, sprinkle the shredded mozzarella and provolone over the meatballs, and scatter the chopped fresh oregano on top. Bake uncovered until the cheese is melted and golden, about 10 minutes.
Let the dish rest briefly, then serve the meatballs topped with additional fresh oregano and with your favorite pasta if desired.