In a large skillet, heat olive oil over medium heat. Add breakfast sausage, cooking until browned, about 5-7 minutes. Stir in diced onion and red bell pepper, sautéing until soft, about 3-4 minutes. Remove from heat and let cool slightly.

In a large mixing bowl, combine the cooled sausage mixture with cream cheese, grated white cheddar, paprika, and sliced green onions. Mix until smooth.

Take stale croissants, slice them in half lengthwise, and arrange the bottom halves in a greased 9x13 inch baking dish. Spread the sausage and cheese mixture over the croissant bottoms, then place the top halves back on top.

In a separate bowl, whisk together eggs, half-and-half, Dijon mustard, hot sauce, and a pinch of salt and pepper until smooth.

Pour the custard mixture over the layered croissants, ensuring it seeps in. Reserve about a cup for topping later. Cover and let it rest in the fridge for at least 1 hour or overnight.

Preheat the oven to 375°F (190°C). Remove cover and brush the tops with reserved custard. Sprinkle with Everything Bagel seasoning and additional cheese. Cover with foil and bake for 30 minutes, then remove foil and bake for another 15-20 minutes until golden.

Let the casserole cool for about 10 minutes before slicing into squares and serving warm.