Preheat oven to 180°C (fan-forced).
Cook the bacon: Place bacon rashers on a lined baking tray and bake for about 10 minutes, or until lightly crisp but still flexible.
Prepare the filling: In a bowl, whisk together the eggs, cherry tomatoes, mushrooms, red onion, parsley, and feta.
Assemble the cups: Line 5 holes of a muffin tin with a rasher of bacon around the sides. Pour the egg mixture evenly into each cup.
Bake: Bake for 15–20 minutes, or until the eggs are set and lightly golden on top.
Serve: Allow to cool slightly before removing from the tin.