Preheat oven to 325°
Lightly coat an 8x8 inch baking dish with cooking spray or butter
Break up English Muffins into chunks and place on bottom of dish
Sprinkle ½ cup of cheese over the English Muffins
Heat skillet over medium high heat and melt 1 tablespoon butter
Sauté peppers and onions in the skillet for 5-6 minutes, or until softened
Add mushrooms to skillet and sauté for 5 more minutes
Next, add 1 cup of spinach to skillet and sauté until wilted, about 2-3 minutes
Spread pepper, mushroom, spinach mixture on top of cheese and muffins, then sprinkle evenly with basil
In a large mixing bowl, whisk together eggs, milk, black pepper, garlic powder, and dijon mustard
Pour this combination over the veggies, cheese and muffins
Bake at 325° for 1 hour or until edges start to slightly brown
Serve warm!