Heat olive oil in a large skillet over medium. Add red onion and cook 3 minutes. Add garlic, oregano, and red pepper flakes; cook 60 seconds.
Stir in sun-dried tomatoes and chickpeas. Cook 2 minutes.
Add vegetable broth and bring to a boil. Add orzo and stir immediately. Season with salt and pepper. Reduce to a vigorous simmer.
Cover and cook 8 minutes. Add kalamata olives, stir, and cook 4–6 more minutes until orzo is al dente.
Remove from heat. Stir in spinach if using. Squeeze lemon juice over the pan and toss gently.
Divide into bowls and crumble feta over each serving. Scatter parsley and serve immediately.
