Cook orzo according to package directions.

Add spinach to the orzo during the last minute of cooking.

Drain the orzo and spinach and rinse with cold water to stop the cooking process.

In a mixing bowl, combine red onion, feta cheese, olives, and pine nuts.

Add the cooked orzo and spinach to the mixing bowl.

In a separate small bowl, whisk together olive oil, balsamic vinegar, salt, pepper, and cayenne pepper (if using).

Pour the dressing over the orzo mixture.

Toss to combine all ingredients.

Taste and adjust seasoning as needed.

Serve at room temperature.