Use a medium (or large) pan to heat the olive oil over medium-high heat.
Add garlic and onion, then cook until it softens.
Add the chopped mushrooms and adjust the heat to medium.
Cook for about 8 minutes --- mixing often.(Note: Some mushrooms would have brown edges at this point.) Add the bell pepper, celery, cayenne powder, thyme, salt, and ground black pepper.
Mix and cook for 2 minutes.
Pour the stock and crushed tomatoes, mix, then cover.
Adjust the heat to medium-high and bring to a boil.
Add the potatoes, mix to combine, then place the lid back on.
Adjust the heat to low and simmer until the vegetables soften.
Add the Worcestershire sauce and stir --- taste, then adjust the seasoning as preferred.
Continue simmering until the vegetables are fully cooked.
Pour the cornstarch mixed with water and mix.
Cover and cook for about 2 more minutes, then remove pan from heat.
Transfer your potato stew with mushrooms into serving bowls --- and serve!