Preheat your oven to 400°F. This ensures it's ready when your frittata mixture is prepared.

Prep all your ingredients before you start cooking - dice the vegetables, chop the bacon, and have everything measured out. This makes the cooking process smooth.

In a 10-12 inch cast iron skillet, cook the chopped bacon over medium heat until crispy, about 6-8 minutes. Use a slotted spoon to transfer the bacon to a paper towel-lined plate, leaving the rendered fat in the skillet.

In the same skillet with the bacon fat, sauté the vegetables one at a time, giving each 2-3 minutes to develop color and flavor. Start with the onion, then add the garlic, followed by the bell peppers, and finally the mushrooms. Don't rush this step - the caramelization adds so much flavor.

Add the cooked bacon back to the skillet with the sautéed vegetables. Stir in the chopped arugula and let it wilt slightly, about 30 seconds.

In a separate bowl, whisk together the eggs, heavy cream, black pepper, kosher salt, and shredded cheddar cheese until well combined and slightly frothy.

Pour the egg mixture over the vegetables and bacon in the cast iron skillet. Give it a gentle stir to distribute everything evenly, then let it sit undisturbed for 1 minute to start setting on the bottom.

Transfer the skillet to the preheated oven and bake for 11-13 minutes, until the eggs are just set in the center but still slightly jiggly. The frittata will continue cooking from residual heat.

Remove from the oven and let cool for 5 minutes before slicing. This resting time allows the frittata to set completely and makes slicing cleaner.