Preheat oven to 400 degrees, position rack in middle of oven.
Whisk eggs in large bowl.
Heat oil in 10 inch oven safe skillet, over medium heat until shimmering.
Add onion and cook until begins to soften, about 4 minutes.
Add broccoli and cook until warmed through, about 2 minutes.
Season with salt and pepper.
Pour eggs over vegetables and cook, gently lifting and pushing cooked edges toward center, allowing eggs to space, about 4 minutes.
Sprinkle cheddar and transfer pan to oven.
Bake until frittata is golden brown and puffed up, 12 – 15 minutes. (It will be slightly soft in the
center)
Transfer to cutting board and cut into 8 wedges.
Serve & Enjoy.