Preheat the oven to 400 degrees Fahrenheit and line a large shallow oven tray with baking paper. Add the ground turkey to a large mixing bowl along with the garlic powder, salt, pepper and Italian seasoning. Use your hands to mix the ingredients together well.
Turn the ground meat out onto the lined oven tray. Press down gently to form a circle – roughly a half inch thick. Transfer to the oven to bake for 15 minutes. Remove from the oven and drain away any excess liquid.
Whilst the base is cooking, thinly slice the onion. Heat half the olive oil in a skillet over a low/medium heat. Add the onion, sweating gently until tender and translucent.
Spread the tomato paste in an even layer across the base of the pizza. Slice the mozzarella into half inch thick discs. Arrange the mozzarella across the pizza.
Slice the olives in half and roughly tear the prosciutto. Arrange across the pizza along with the cooked onions. Season with a little salt and pepper. Transfer to the oven to bake for a further 10 minutes or until the base is completely cooked through and the cheese has melted.
Scatter with the fresh arugula. Drizzle with the remaining olive oil to serve.