Prepare a large pot of boiling salted water. Add several heavy pinches of salt to the water after it starts to boil. Add the diced chicken thighs and cook them until they are fully cooked for about 15 minutes. It is ok if they are overcooked as it will help make them more tender. Drain them, reserving the water it was cooked in for chicken broth.
Heat a large nonstick skillet over medium high heat until hot. Add the salted butter and heat until the butter is all melted. Swirl the pan to distribute the butter evenly. Add the sliced baby portobello mushrooms and saute until nicely browned, about 3-4 minutes.
Next, add the cream and reserved chicken broth. Bring the mixture to a simmer and allow to simmer for 1-2 minutes over low heat.
Add the cooked chicken, drained pimento peppers and spinach. Cook until everything comes together and the spinach is wilted, about 1-2 minutes.
Sprinkle xanthan over the top and stir immediately. Cook until thickened.Serve the dish over shirataki noodles, zucchini noodles or low carb bread.