Mix oatmeal, wholemeal flour, plain flour, yeast, and salt in a bowl.
Gradually stir water into the center until the batter reaches the consistency of thick cream.
Cover and set aside for 3 to 8 hours to develop gluten.
Whisk in the baking powder once the batter has rested.
Heat 5ml of vegetable oil in a frying pan and add a ladle of batter.
Fry the oatcake for 1 to 2 minutes until golden-brown on one side.
Flip and fry for another minute until golden on both sides.
Keep cooked oatcakes warm on a plate separated by greaseproof paper.
Preheat the grill to its highest setting.
Grill bacon rashers for 3 to 4 minutes per side until crisp.
Heat olive oil in a pan and fry mushrooms for 3 to 4 minutes until brown.
Return an oatcake to a hot pan and sprinkle cheese over one half.
Add two bacon rashers and a spoonful of mushrooms once the cheese begins to melt.
Fold the oatcake and heat for one more minute until the cheese is fully melted.
Repeat for all remaining ingredients and serve immediately.