Prepare Seafood and Aromatics:
Defrost shrimp and scallops; take off tails and shells. Blot dry. Finely chop garlic. Grate lemon zest, then squeeze the juice.Cook Spaghetti:
Fill a large pot with water and bring to a boil. Cook spaghetti as directed on the package. Drain.Sear Scallops:
Meanwhile, in a large pan over medium-high heat, warm 1 Tbsp olive oil. Sear scallops for 2 minutes per side until they turn opaque and get a light brown crust. Transfer to a plate.Cook Shrimp:
Using the same pan, cook shrimp for 1-2 minutes per side until they become opaque and pink. Set aside with the scallops.Sauté Garlic and Vegetables:
Add another 1 Tbsp olive oil to the pan and lower the heat a bit. Sauté garlic for 2 minutes. Toss in tomatoes and cook for 5 minutes, letting them burst and release juices. Add spinach and cook until it wilts, roughly 2 minutes.Combine Pasta and Seafood:
Remove pan from heat. Mix in the cooked pasta, seafood, lemon juice, lemon zest, red pepper flakes, and the remaining 2 Tbsp olive oil. Season with salt and pepper, toss everything together. Adjust seasoning as needed.Top with Parmesan:
If desired, top with freshly grated Parmesan before serving.