Start boiling water to cook the pasta.
Wipe mushrooms clean and slice about 1/3 inch thick (1 cm).
Slice onion and peppers into thin slices.
Melt the butter and oil together in a large skillet over medium-high heat. Add mushrooms and cover. Cook 60-90 seconds until browned.
Stir and add onions, peppers, and garlic and salt and pepper. Saute for several seconds. Cover and cook about 2 minutes, until the onions and peppers are softened.
Add Worcestershire, soy sauce, oregano, mustard and stir until the liquid has mostly evaporated. Turn off the heat.
When the noodles are cooked, reserve 1/2 cup of cooking water (use a mug to dip some water from the pot) then drain.
Add the noodles and half the reserved cooking water and the sour cream to the vegetables. Turn heat to low and stir until water is absorbed and cheese is melted. Add more water if you need to get the cheese moving.
Turn off heat. Stir in spinach and Cheddar.