Cook Ziti pasta in boiling water as per package instructions. Drain and set aside.
In a large pan or pot, saute garlic and onion in oil over medium heat until aromatic. Add the salami and cook while stirring from time to time until slightly browned.
Pour in the diced tomatoes and tomato sauce. Add the Italian seasoning, chili flakes, and season with salt as needed. Stir and simmer for 5 minutes.
Turn off the heat and add the cooked ziti to the sauce. Toss together until all pieces are well coated with sauce. Set aside.
In a saucepan, melt butter over low heat. Add the flour and stir until well mixed. Gradually add milk while stirring constantly to prevent lumps from forming.
Once all the milk is added and sauce starts to thicken, add the grated Parmesan cheese. Stir again until it becomes smooth and no more lumps are visible. Remove from heat.
Add the sour cream and salt to the sauce. Pour half of the white sauce to the pasta and toss to mix.
Transfer the pasta to a 13x9-inch baking dish and pour the remaining white sauce on top. Sprinkle the shredded mozzarella evenly on top of the sauce.
Bake at 180°C for 20-30 minutes until cheese has melted and bubbly.