1. Spray a large nonstick skillet with nonstick cooking spray;heat. Add the chicken and cook, turning as needed until brown,5-6 minutes, transfer to a plate.
2. Preheat oven to 375F.
3. Spray skillet with more cooking spray. Add the onion and garlic;cook,stirring as needed, until softened, anout 5 minute. Add the tomotoes, Italian seasoning and pepper; bring to boil. Reduce the heat and simmer, uncovered, stirring as needed, until the mixture is thickened slightly, 8-10 minutes.
4. Meanwhile, cook the ziti, drain and mix with ricotti cheese.
5. Pour half of the tomotoe mixture into a 13x9 baking pan, layer with the ziti mixture, the chicken and the remaining tomoto mixture. Sprinkle with cheese. Bake until hot and bubble about 15-20 minutes.