01 - Preheat your oven to 425°F (220°C). Line a baking sheet with parchment paper for easy cleanup.
02 - In a large mixing bowl, combine the ground turkey, breadcrumbs, Parmesan cheese, egg, minced garlic, parsley, oregano, salt, and black pepper. Mix gently until just incorporated. Shape the mixture into 16 small meatballs.
03 - Arrange the formed meatballs on the prepared baking sheet. Bake for 12 to 15 minutes, or until they are golden brown and cooked through.
04 - While the meatballs are baking, toss the cubed bread with olive oil, minced garlic, and salt. Spread the bread cubes on a separate baking sheet and toast them in the oven for 7 to 10 minutes, stirring halfway through, until golden and crisp.
05 - In a large saucepan, warm the marinara sauce over medium heat until it begins to simmer. Gently add the baked turkey meatballs to the simmering sauce and let them cook together for 2 to 3 minutes.
06 - Divide the baby spinach or arugula evenly among four serving bowls. Arrange a portion of the saucy meatballs on top of the greens. Sprinkle shredded mozzarella cheese over the warm meatballs to allow it to melt.
07 - If using, add the sliced pepperoncini or pickled banana peppers. Finish by scattering the toasted garlic bread croutons over each bowl. Serve immediately for the best texture and flavor.