First, grab a large, microwave-safe coffee mug. Coat the inside thoroughly with cooking spray or a small amount of butter. This step is crucial because it creates a non-stick surface, allowing the cooked egg to slide out easily without a messy cleanup.
Crack the egg directly into your prepared mug. Add the milk or water, along with a pinch of salt and pepper. Use a fork to whisk the mixture vigorously until the yolk and white are fully combined and it looks slightly frothy.
Now it's time to add your veggies and cheese. Gently stir the diced vegetables and shredded cheese into the egg mixture. Mix just enough to ensure all the ingredients are evenly distributed throughout the mug for a flavorful bite every time.
Place the mug in the microwave and cook on high for 60 to 90 seconds. The egg will puff up significantly—this is completely normal! All microwaves vary, so check after 60 seconds. The egg should be set but still moist.
While the egg cooks, warm your tortilla in the microwave for about 15 seconds. Once the egg is done, carefully remove the hot mug. Run a fork around the edge to loosen the egg, then scoop it onto your warm tortilla, fold, and enjoy immediately.