Add bacon to a large skillet set over medium heat. Cook, stirring frequently, until crispy, approximately 10 minutes. Transfer cooked bacon with a slotted spatula to a plate lined with paper towels. Set aside.

Leave 2 tablespoons of bacon grease in the skillet and return to heat. Add the red onion and cook, stirring occasionally, until soft, approximately 3-4 minutes.

Add apple cider vinegar, honey and Dijon mustard. Season with salt and black pepper, to taste. Stir to combine. Cook, stirring constantly, until thoroughly emulisfied and heated through, approximately 2 minutes.

Reduce heat to low and stir bacon and extra virgin olive oil into the skillet until combined. Continue simmering on low heat while preparing the salad.

Place spinach leaves in a large bowl. Top with sliced strawberries and crumbled feta cheese. Drizzle hot bacon dressing generously over the salad while it's still warm to wilt the spinach slightly. Season with salt and black pepper to taste.