In a skillet, warm one tablespoon of oil. Saute onions and mushrooms until soft. Then add spinach until completely wilted. Remove vegetables from pan to bowl for the time being.
Add remaining oil to skillet. Bring to temperature and add sausage. (I originally used 3 Gilbert Sausages, which equals 7.5 ounces. I've also used a similar amount of cooked breakfast patties.) Cook 8-10 minutes until cooked through. Remove from stove and allow to cool before slicing.
Grease a 9 x 13 casserole dish and add bread, vegetables, sausage and cheese.
In a large bowl, whisk eggs, milk, salt, pepper, dried parsley and minced garlic. Pour egg mixture over bread, veggies, sausage and cheese. Refrigerate pre-baked strata at least two hours, preferably overnight.
Remove casserole from fridge and allow to come to room temperature. (Preferably for an hour.) Meanwhile, preheat oven to 375 degrees. (Last time I made this I drizzled a bit of cream over the top before baking to keep it moist.)
Place strata in 375 degree oven and bake for 20 minutes. Then, place foil over strata and bake for an additional 30 minutes covered. Remove from oven when casserole is completely set.
Allow strata to rest for 10 minutes before serving, so you don't burn your mouth. Serve with an extra sprinkling of cheese if desired.