Position a rack in the center of the oven and preheat to 350°F.
Heat an 11-inch ovenproof non-stick skillet over medium high heat. Add the pancetta and cook until crispy, 3-5 minutes, flipping occasionally. Remove the pancetta to a paper towel lined plate and set aside.
Add the sausage to the skillet and cook in the pancetta fat over medium heat until beginning to brown. 2-3 minutes. Add the onion, jalapeno and cook until the sausage is browned, and the onion is translucent. 4-5 minutes. Transfer to a bowl with a slotted spoon.
Whisk together the eggs, milk, half-and-half, cayenne, salt, and pepper in a large bowl. Add in the sausage mixture and stir to combine. Add the bagel tops and let them soak for 5 minutes.
Lay out the bagel bottoms (cut side up) on a board or plate. Layer each bottom with a few pieces of spinach, a sprinkle of provolone, and a pancetta round. Place the bottoms into a lightly oiled 11-inch NonStick skillet. Spread the rest of the spinach and provolone around the skillet. Place one of the bagel tops onto each of the bagel bottoms, then pour over the egg mixture, spreading the sausage mixture into the space between the bagels.
Carefully place the skillet into the preheated oven (it will be quite full). Bake for 55 minutes. Raise the temperature to 400°F and bake until the casserole is puffed, golden brown at the edges and set in the center, about 15 minutes more.
Turn on the broiler and broil for 2-3 minutes to lightly brown the top. Watch this step carefully, as you don’t want to it to burn.
Remove from the oven and let stand for 10-15 minutes before serving.
