For quicker, more even cooking, slightly flatten breasts with a kitchen mallet. If they are very thick, slice them in half horizontally before flattening. Season with salt and pepper.
Heat a skillet over high heat. When pan is hot, add 1 tablespoon oil.
When oil is hot, put chicken in pan and cook until golden brown on both sides and cooked through. Remove chicken from pan and slice.
Add remaining tablespoon oil to pan. Add onions and cook until softened.
Add mushrooms and cook until golden brown.
Add the red pepper and garlic, stir, and cook for about 2 minutes.
Deglaze pan with water and bouillon cube, scraping bottom to release any bits sticking to the bottom of the pan.
Add cream and thyme. Bring to a simmer. Let simmer 2-3 minutes then turn off heat.
Add parmesan slowly, whisking constantly until melted.
Salt and pepper to taste.
Add sliced chicken and parsley to sauce, then toss with pasta.
Serve.