You start by making a traditional béchamel-based cheese sauce, then stir in chopped or shredded cooked chicken, tomato sauce, and a bit of fresh or dried oregano.
Preheat the oven to 375°F (190°C). Generously spray a 12-cup muffin pan with cooking spray.
Bring a large saucepan filled with water to a boil over high heat. Add the salt and pasta, reduce the heat to medium, and cook until al dente, about 7 minutes or according to the package directions. Drain the pasta and set aside.
In the same saucepan over medium heat, melt the butter. Add the minced garlic and cook until fragrant (about 1 minute), then add the flour and whisk until smooth. Slowly add the milk while whisking constantly, until smooth. Continuing to whisk, slowly add the cheeses until smooth. Add the chicken, oregano, and tomato to the cheese sauce and stir to combine. Stir in the egg and mix well.
Spoon the pasta mixture into the prepared muffin cups, dividing it evenly and filling the cups. Bake the bites until they are crisp and browned around the edges and bubbling, about 10 minutes. Allow to cool in the pan for about 10 minutes before removing (use a small knife to help dislodge them if necessary). Serve with tomato sauce for dipping, if you like.