Preheat the oven to 375°F (190°C).
Place the chicken breasts between two sheets of plastic wrap and pound them to an even thickness of about ½ inch.
Season the chicken breasts with salt, pepper, garlic powder, and oregano.
Set up a breading station: Place the flour in a shallow dish, whisk the egg in another shallow dish, and place the breadcrumbs in a third shallow dish.
Dredge each chicken breast in flour, dip into the egg, then coat with breadcrumbs, pressing firmly to adhere.
Heat a large skillet over medium-high heat. Add a tablespoon of oil, then cook the chicken breasts for about 4-5 minutes per side until golden brown and cooked through. Remove and set aside.
In a baking dish, place the slider buns cut-side up. On each bun, layer marinara sauce, a piece of chicken, and a generous sprinkle of mozzarella and Parmesan cheese.
Place the sliders in the oven and bake for about 10 minutes, or until the cheese is melted and bubbly.
Remove the sliders from the oven and let them cool slightly before serving. Garnish with fresh basil if desired.