Add the mushrooms and cook for 6-8 minutes, stirring halfway, until browned.
Add a drizzle of oil and the shallots and cook until softened, about 2-3 minutes.
Add dried thyme, red pepper flakes, garlic, and salt and pepper to the skillet. Cook, stirring, for about 30 seconds.
Add the balsamic vinegar and a splash of water. Stir and let liquid evaporate.
Add the butter and let it melt. Mix well. Remove from heat.
Butter the toast and divide the mushrooms between the two pieces.
Add freshly grated Parmesan cheese, and parsley, optional, and serve.
Notes
Use your favorite mushrooms. I love cremini mushrooms so that's what I usually use because I buy them at each grocery shop.Customize this recipe by using onions instead of shallots or dried rosemary or oregano instead of thyme.Try spreading the toast with cream cheese or hummus first.Let the mushrooms cook long enough that they let out their moisture - this results in a really good texture in the mushrooms.Use a sturdy bread on toast your bread extra so it doesn't get soft and soggy. I usually use sourdough bread.