Cook bacon until crispy and cut into bite-size pieces.
In a large salad bowl, toss baby spinach or mixed greens, bacon, red onion, strawberries, feta cheese, and walnuts.
In a bowl or mixer bottle, mix the mayonnaise, vinegar, sugar, onion, dijon mustard, and poppy seeds together. Add salt and pepper if needed.
When ready to serve, toss salad with dressing.
