Bring a large pot of salted water to a rolling boil, tasting like the sea.
Add the spaghetti to the boiling water and cook until just al dente, about 8 minutes, stirring occasionally for even cooking. Meanwhile, rinse the peas and set aside.
While the pasta cooks, heat olive oil in a wide skillet over medium heat until fragrant, about 30 seconds, and the oil starts to shimmer.
Add the minced garlic to the hot oil and sauté until fragrant and lightly golden, about 30 seconds; you should smell a nutty aroma.
Use a colander to drain the pasta and peas, reserving about a cup of starchy pasta water. Add the drained pasta and peas directly into the skillet with garlic and oil.
Toss gently over medium heat, allowing the peas to pop with sweetness and the pasta to absorb the fragrant garlic oil, about 1-2 minutes.
Add the baby spinach and cook for another 1-2 minutes, stirring until wilted and vibrant green.
Sprinkle the lemon zest over the mixture, then splash in a little of the reserved pasta water if the dish seems dry, stirring gently to loosen everything up.
Season generously with sea salt and freshly cracked black pepper, tasting and adjusting as needed. Toss again to combine all flavors evenly.
Transfer the pasta to warmed plates, drizzling with a little extra olive oil or lemon if desired, and serve immediately while vibrant and hot.
