Preheat oven to 425 degrees. Spray mini mini muffin pans with cooking spray and set aside.
Mix eggs and half and half in a medium bowl until combined. Add mustard powder and season to taste with salt and pepper. Set aside.
Melt butter in a small skillet over medium heat; add mushrooms. Saute until mushrooms are cooked and have released most of their liquid. Add ham, garlic and scallions and cook for 2 minutes. Remove from heat.
Divide mushroom mixture evenly among the mini muffin pans. Divide shredded cheese evenly among mini muffin pans. Pour egg mixture over top, being careful not to overfill. Top with grated parmesan cheese. Bake for 13-15 minutes or until golden brown. Remove from oven and serve immediately.