1/2tspcrushed red pepper (cut down to 1/4 tsp if you are very sensitive to heat)
Preheat oven to 400 degrees. Heat olive oil in a 12″ cast iron skillet over medium heat until shimmering, then add onion and mushrooms and season with salt & pepper. Saute for 3 minutes, stirring occasionally, then add in garlic and broccoli and continue sauteing and stirring occasionally until broccoli is bright green and crisp-tender, about 4-5 minutes.
While vegetables are sauteing, whisk together eggs, milk, mustard, thyme, and red pepper until well blended & frothy. Pour the egg mixture into the skillet on top of the veggies and continue cooking over medium heat just until the edges start to set (about 4 minutes).
Turn off the heat on the burner and top your eggs evenly with the shredded cheddar, then move the skillet into the oven and bake at 400 degrees for 15 minutes, or until frittata is set.
Broil for another two minutes to brown, then let your frittata sit for five minutes before slicing.
If you don't yet have a cast iron skillet, they're well worth the minimal investment (just $9.88 at Walmart as I type today!) -- I use mine constantly. I garnished my frittata here with a couple of chopped green onions, but that's totally optional.
Easy Broccoli Mushroom Frittata from Mashup Mom: https://www.mashupmom.com/easy-broccoli-mushroom-frittata-low-carb-gluten-free/