Lightly grease a silicone egg bite mold.
Sauté spinach and bell peppers lightly in a sauté pan with a little oil or cooking spray to wilt the vegetables.
Divide the vegetables evenly in the bottom of the egg molds.
In a blender or food processor, combine eggs, milk, salt, pepper, cheese and mustard. Blend on high speed for 10-15 seconds until eggs, cheese and spices are well blended.
Place silicone mold into the air fryer basket/tray.
Pour egg mixture into silicone mold. Leave a little space at the top of each mold so they don't overflow when cooking.
Cover the mold with a silicone cover or cover loosely with foil if you don't have a silicone lid.
Cook for 10 minutes at 340ºF in the air fryer. Open air fryer and rotate the mold 180º to prevent one side from cooking faster than the other.
Cook covered for 5 more minutes or until egg bites start to pop up.
Remove cover and cook until all 7 of the egg bites have popped up above the mold like a souffle and are cooked through, approximately 1-5 minutes, depending on your air fryer and how full they are.
Allow to cool for 1-2 minutes. Invert the mold onto a plate to remove egg bites.
Serve while warm.