If you’re making these to eat today, preheat your oven to 400 degrees F. If you’re making them ahead to eat later, you do not need to preheat the oven.
Separate each of your bagels into halves. Use a knife, spoon or your fingers to hollow out the bottom half of each bagel. Set bread aside to use for breadcrumbs in another recipe.
In a medium bowl, whisk together the eggs, spinach, pesto and salt. Heat a medium skillet over medium heat. Spray with nonstick spray. Add egg mixture; cook and stir until eggs are fully cooked. Remove from heat.
Assemble your breakfast sandwiches by dividing the cooked eggs between the four bagels, filling the hollowed out portion of each bagel. Top with cheese (cut a hole in the middle of the cheese, if you’d like), then bacon and top with the other half of the bagel.
To eat now, wrap each of the breakfast sandwiches in foil and bake for 10 minutes. To save for later, wrap each of the breakfast sandwiches in foil and place in the freezer for up to 2 weeks. To reheat, take a sandwich out of the freezer while you preheat your oven to 400 degrees F. Bake the frozen bagel sandwiches for about 30 minutes. Grab and go!