Start boiling the spaghetti in well salted water.

Slice the chicken thighs into large chunks, about 1/2" by 1". Sear very well in a heavy skillet with olive oil. If the chicke came with skin, render some of the fat instead of the olive oil.

Set chicken aside and cook the onions in the pan, adding a splash of water to loosen any chicken fond.

Set onions aside with the chicken and sear the mushrooms. A splash of olive oil is likely needed. Let them sit until dark brown on one side then cook the other side similarly.

Add the mushrooms and chicken back to the pan and toss with the radicchio. Turn the pan off and leave it until the pasta is ready.

When the pasta is cooked through, drain and reserve 1/4 cup of pasta water. Mix the spaghetti, pasta water, a few grinds of pepper, and then mix half the parmesan in, then the other half.

Gently fold half of the ingredients in and top with the other half. This will help prevent all of the ingredients from sinking to the bottom as it is served.