In a small bowl, combine the ricotta cheese, lemon zest, 3 tablespoons of the chives, and a pinch of salt and pepper. Stir gently until just blended and set aside.
Heat the olive oil in a large non-stick skillet over medium heat until it shimmers.
Carefully crack the eggs into the skillet and season them with the remaining salt and pepper. Cook for 3 to 4 minutes, or until the egg whites are fully set and the yolks are still soft and runny.
While the eggs cook, toast the sourdough slices until they are golden brown and crisp.
Spread a generous 1/4 cup of the ricotta mixture evenly onto each piece of warm toast.
Gently place one cooked egg on top of each ricotta-covered toast slice. Garnish with the remaining chopped chives and a light sprinkle of red pepper flakes before serving immediately.