Rinse the spinach leaves thoroughly and pat them dry.
In a large bowl, add the fresh spinach.
Chop the cherry tomatoes in half and add them to the bowl.
Thinly slice the red onion and add it to the salad.
Dice the cucumber and mix it in with the other ingredients.
Crumble the feta cheese over the salad.
Chop the walnuts and sprinkle them on top.
In a small bowl, whisk together the olive oil and balsamic vinegar.
Drizzle the dressing over the salad and toss gently to combine.
Season with salt and pepper to taste. Serve immediately.