Wash the spinach leaves thoroughly under cold water.
Pat the spinach dry using a clean kitchen towel or salad spinner.
In a large salad bowl, add the fresh spinach as the base.
Halve the cherry tomatoes and add them to the bowl.
Slice the cucumber and add it to the salad.
Thinly slice the red onion and sprinkle it over the salad.
Crumble the feta cheese and distribute it evenly on top.
In a small bowl, whisk together olive oil and balsamic vinegar.
Drizzle the dressing over the salad, ensuring even coverage.
Season with salt and pepper to taste, then toss gently to combine.