Heat a dutch oven, or large oven safe heavy bottomed pot over medium high heat. Add 1 Tbsp oil and 1 Tbsp butter and let butter melt. Add beef pieces in an even layer – do not overcrowd. Work in batches if necessary. Stir fry beef for 60-90 seconds. Don't cook any longer or they'll be overcooked and tough. Remove to a plate.
Add remaining 1 Tbsp of oil and 1 Tbsp of butter to hot pot, then add mushrooms, onions and green pepper. Cook, stirring occasionally, 5 minutes or so, until tender and mushrooms have browned. Season with thyme and a pinch of salt and pepper.
Pour in beef stock and water, bring to a boil. Add pasta, reduce heat so liquid is at a gentle boil, and boil for approximately 12-15 minutes. Stir pasta frequently to prevent the pasta from sticking to the bottom of the pot.
When most of the liquid has been absorbed, turn off the heat. Chop 5 slices of provolone cheese and add to the sour cream, cream cheese & cooked beef. Stir well to combine. Add salt & pepper to taste.
Top pasta with remaining provolone slices and broil for 2-3 minutes, until cheese is toasted, melted and bubbly. Sprinkle with minced parsley.