Lightly mist a deep frying pan with cooking spray and cook the onion over a medium heat for 4-5 minutes until softened. Add the garlic, season well with salt and black pepper, then cook 1 minute.
Add the mushrooms with a splash of water and turn the heat up slightly. Cook 4-5 minutes, stirring often, until golden.
Reduce the heat, add the soft cheese and stir until it melts. Pour in the stock, season with black pepper and cook 8-10 minutes until slightly thickened.
Cook the pasta according to pack instructions. Drain well and stir through the spinach to wilt.