Boil a large pot of salted water, add spaghetti, and cook for 8–10 minutes until al dente. Reserve pasta water before draining.

In a large skillet, heat olive oil and butter over medium heat. Add shrimp and sauté for 2–3 minutes until pink. Add minced garlic and red pepper flakes, cooking for another minute.

Lower the heat and add drained spaghetti, lemon juice, and reserved pasta water. Toss gently for about 2 minutes until well-coated.

If using, fold in spinach or cherry tomatoes and cook for an additional 2–3 minutes until the spinach wilts and the tomatoes soften.

Remove from heat, plate the pasta, and add an extra pat of butter. Garnish with parsley if desired before serving.