Clean, trim and quarter the mushrooms. Dice bacon. Peel onions and cut into fine sticks. Heat oil in a coated pan. Leave the bacon in it until crispy, take it out.
Fry the mushrooms and onions in hot frying fat while turning for 3-4 minutes, season with salt and pepper and remove. Mix onions, bacon, mushrooms and crème fraîche, season with salt and pepper. Cut off the stalk of the bell peppers about 1 1/2 cm thick as a lid.
Remove the seeds and wash the peppers. Cut the pepper straight at the bottom so that it stands upright. Fill the bell peppers with the mushroom-onion mixture. Place in a casserole dish and pour in the stock. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 20 minutes.