1.In a medium sauté pan over medium to high heat, add pepperoni and cook until crispy; remove and drain on paper towels. When cool, crumble pepperoni, divide 3/4 for tossing in stuffing, and 1/4 for garnish. Leave remaining grease in pan, add yellow onions, pepperoncini, red pepper, celery, garlic, and sun-dried tomatoes, and sauté until onions are translucent. Remove and let cool.
2.In a large bowl add focaccia cubes, parsley, and green onions. In a small bowl add eggs, pepper, paprika, and whisk. Pour eggs over bread, add sautéed vegetables, and crumbled pepperoni. Mix all ingredients thoroughly and slowly add chicken stock, allowing for it to absorb evenly.
3.Preheat oven to 350 degrees. Lightly butter a 13" x 9" pan and add mixture to pan. Cover with aluminum foil and bake for 35 minutes; remove foil and bake for another 15 minutes to brown the top.
4.Garnish with Parmesan cheese and additional pepperoni crumbles.