Bring a large pot of water to a boil and salt it generously.
While waiting for the water to boil: In a large skillet, bring the frozen peas, cream, red pepper flakes garlic and salt to a simmer over medium heat. Cover skillet, reduce heat to medium-low and simmer until peas are tender, about 5 minutes. *If your skillet doesn't have a lid, place a large baking sheet over-top of the skillet to cover. Be careful removing. It gets hot!
Remove lid from the skillet and add the spinach. Cook, stirring, over medium-low heat, until the spinach is wilted. Remove the skillet from the heat and stir in the lemon zest and juice.
When water is boiling, add gnocchi and boil until gnocchi floats to the top, about 2 minutes. Remove gnocchi to skillet with a large slotted spoon (reserving the gnocchi cooking water). Add Parmesan to the skillet as well as splash of the gnocchi cooking water. Return the skillet to the heat and cook, stirring, until just re-warmed through, adding a bit more gnocchi cooking water if necessary to thin out the sauce.
Spoon into bowls. Season well with salt and freshly ground pepper and garnish with a bit more lemon zest, if you like.
Be sure to read the "Cook's Notes" included with this post, where I share some valuable tips, options, substitutions and variations for this recipe!