Preheat the oven to 350°F (180°C). Grease a 12-cup muffin tin with cooking spray.
Dice the bell peppers and mushrooms. Chop the spinach.
In a mixing bowl, whisk together the eggs and heavy cream/Almond Milk until well combined. Season with salt and pepper to taste.
Divide the diced vegetables and shredded cheese evenly among the 12 muffin cups. Pour the egg mixture over the vegetables and cheese, filling each cup almost to the top.
Place the muffin tin in the preheated oven and bake for about 20-25 minutes, or until the mini omelettes are set and slightly golden on top.
Remove from the oven and let them cool slightly before using a knife to loosen the edges and remove the mini omelettes from the tin. Serve warm!