Heat butter in a skillet over medium heat. Add garlic, zucchini, and red pepper flakes and fry until zucchini are tender. Add spinach, lemon zest, and half the dill and cook until spinach is wilted. Remove from heat and season with salt and pepper.
Divide the zucchini-spinach mixture into four small oven-proof dishes or ramekins, pour 1/4 of the cream into each ramekin or dish, then crack an egg into each. Sprinkle feta cheese over each egg, dividing evenly.
Bake in the oven until egg whites are set, about 12-14 minutes. Garnish with remaining dill.