Start by preheating your oven to 350°F (175°C). Slice the tops off the bagels, about 1/3 of the way down, and gently hollow out the centers. Be careful to leave a 1/2-inch thick wall and avoid tearing the bottom.
In a mixing bowl, whisk together the eggs, milk, salt, pepper, and smoked paprika. Once combined, stir in the shredded cheese, cooked bacon, spinach, bell pepper, and green onions. This mixture will be the heart of your stuffed bagels.
Line a baking tray with parchment paper and arrange the hollowed-out bagels on it. Carefully pour the quiche mixture into each bagel cavity, filling them almost to the top. Don’t overfill to avoid spills during baking.
Bake the bagels in the preheated oven for 25–30 minutes, or until the egg mixture is set and slightly golden on top. Let them cool for a few minutes before serving to allow the filling to set.