Cook the spaghetti in a large pot of salted boiling water according to package instructions, about 8-10 minutes. Reserve ¼ cup pasta water, drain and toss with 1 tbsp olive oil.

In a large skillet, heat 1 tbsp olive oil over medium-high heat, add diced red onion, and sauté for 4-5 minutes until softened.

Add minced garlic and cook for an additional minute until fragrant.

Add halved cherry tomatoes and remaining olive oil. Cook for 3-4 minutes until tomatoes soften.

Stir in baby spinach and cook for 2-3 minutes until wilted.

Add kalamata olives, lemon juice, red wine vinegar, oregano, salt, and pepper. Cook for another minute.

Remove from heat, combine with reserved spaghetti, toss well, and fold in feta cheese and basil.

Garnish with fresh basil or parsley and serve warm or chilled.