In a large pot, bring salted water to a rolling boil over high heat. Add spaghetti and cook according to package instructions until al dente, about 8-10 minutes. Reserve ¼ cup of pasta water, then drain and set aside.

Heat a large skillet over medium heat and add butter. Once melted, add minced garlic and sauté until fragrant, about 30 seconds. Add thawed shrimp, seasoning with salt and pepper. Cook for 3-4 minutes until shrimp turn pink and opaque.

Add grape tomatoes to the skillet and cook for 2-3 minutes until softened. Add fresh spinach and stir until wilted, about 1-2 minutes.

Toss in cooked spaghetti and reserved pasta water. Mix everything gently, ensuring the spaghetti is well coated in the sauce. Cook for an additional 1-2 minutes, allowing flavors to meld.

Remove from heat and serve immediately. Top with grated cheese or crushed red pepper flakes if desired.