Heat 2 tablespoons oil in a pan over medium heat. Add the garlic and green onion, and fry for 3-4 minutes. Then add the shredded chicken, crushed tomatoes, ketchup, 2 teaspoons oregano and black pepper. Cook for 5-7 minutes. Taste, adjust seasonings and set the chicken mixture aside.
Preheat oven to 350 degrees F. Line 2 baking sheets with parchment paper. Place the bread slices on the baking sheet and toast in the oven until a little crispy, about 5-8 minutes, toasting time depends on how thick the slices are (keep a close watch on them).
Place a layer of shredded mozzarella cheese on each slice.
Then place a layer o the chicken mixture and top with the mozzarella cheese. Sprinkle with dried oregano leaves.
Bake in the preheated oven until cheese is melted. Serve immediately.