Rinse the spinach leaves thoroughly and pat dry.
Place the spinach in a large salad bowl.
Slice the strawberries and add them to the bowl.
Chop the walnuts and sprinkle them over the salad.
Crumble the feta cheese on top of the salad.
Thinly slice the red onion and add it to the mix.
In a small bowl, whisk together the olive oil and balsamic vinegar.
Season the dressing with salt and pepper.
Drizzle the dressing over the salad just before serving.
Toss gently to combine all ingredients.