Bring a large pot of salted water to a rolling boil. Add the pasta and cook until al dente, about 8 minutes. Drain, reserving a cup of pasta water, and set aside.
While the pasta cooks, heat olive oil in a large skillet over medium heat until shimmering and fragrant.
Add the minced garlic to the skillet and sauté for about 1 minute, until it becomes fragrant and lightly golden, but not browned.
Add the fresh spinach to the skillet and cook, stirring occasionally, until wilted and vibrant green, about 2 minutes. The spinach should be tender but still bright.
Reduce the heat to low, then crumble the feta cheese into the skillet. Stir gently to let it melt slightly and coat the greens, creating a creamy mixture.
Add the drained pasta to the skillet and toss to combine everything evenly. If the mixture seems dry, stir in a splash of the reserved pasta water to loosen and create a silky sauce.
Finish by squeezing the lemon juice over the pasta and sprinkling red pepper flakes for a subtle kick. Toss once more to distribute the flavors evenly.
Turn off the heat and let the pasta sit for a minute to allow the flavors to meld. Taste and adjust seasoning if needed.
Serve immediately, garnished with extra feta crumbles or a drizzle of olive oil if desired. Enjoy the vibrant, creamy, and tender pasta while hot.
