Preheat the oven to 180 degrees Celsius/ 360 degrees Fahrenheit.
Cook the pasta according to the packet's instructions. Drain and return to the pot.
Cook the bacon.
If using fresh mushrooms, clean them with kitchen paper, slice them thinly and fry them in the pan you used for frying the bacon for about 3-4 minutes, until the water they release evaporates and they are golden. You will not need to add fat if there is still some bacon fat in the pan.
If using mushrooms from a jar, let them drain well.
Cube the cooked chicken.
Add the crumbled or chopped bacon, chicken, and mushrooms to the pasta in the pot.
Add salt, pepper, dried rosemary, sweet paprika powder, and garlic powder.
Add the sour cream and ¾ of the grated cheese. Mix well and adjust the taste with salt and pepper, if necessary.
Place the chicken and bacon pasta in a casserole dish of about 19x23 cm/7.5x9 inches.
Sprinkle the dish with the remaining grated cheese.
Bake in the preheated oven for 20-25 minutes or until the top of the chicken and bacon pasta bake is golden brown.
Sprinkle with chives and serve.