You wouldn't normally think of a salad as being comfort food, but this is a salad you can really cozy up to thanks to the warm bacon and cider dressing. The warm dressing wilts the spinach so it is softened but retains its shape and toothsomeness. I am also comforted by this salad because even though it is decadent- with bacon- I can relax knowing I don't have to feel the least bit guilty about eating it.
Place spinach into a large bowl. Cook bacon in a large skillet over medium heat for about 4 minutes, or until it is just crispy. Add Canadian bacon to the skillet and cook for 2 more minutes, stirring frequently. Remove meat from pan and place on a plate lined with paper towels. Drain any remaining fat from the skillet. Add olive oil and onions to the skillet and cook for about 2 minutes, or until onions soften slightly.
Add mushrooms to the pan and cook, stirring frequently, for 2 more minutes. Put onions and mushrooms on top of the spinach. Add apple cider and vinegar to the skillet and turn the heat up to medium-high. Stir to scrape up any bits that are stuck to the bottom of the pan and cook for 8 to 10 minutes or until cider is reduced to about 1/2 cup. Whisk in mustard, salt and pepper, to taste.
Pour warm cider dressing over the mushrooms and spinach and toss until the vegetables are well coated. Sprinkle the bacon on top and serve.