Preheat oven to 375° F.
Heat the oil in a medium non-stick skillet over medium heat.
Add the mushrooms to the pan and cook until softened. Set aside.
In a large bowl, whisk together the eggs, milk, salt, and pepper until combined. Add the English muffin cubes to the bowl and toss to coat.
Stir in the mushrooms.
Divide the mixture evenly between 4 8-ounce ramekins coated with cooking spray and place on a baking sheet.
Bake the strata for 25-30 minutes or until puffed and golden brown. Allow to cool for 5 minutes before serving.