Preheat oven to 350°F. Lightly grease a 9x13-inch baking dish or line it with parchment paper.
Unroll one can of crescent roll dough and press it into the bottom of the baking dish, sealing any seams.
In a medium bowl, beat the softened cream cheese, sugar, vanilla, salt, and lemon zest (if using) until smooth.
Stir in the mini dark chocolate chips.
Spread the cream cheese mixture evenly over the crescent dough in the pan.
Unroll the second can of crescent dough and place it over the top, gently pressing to seal.
Brush the melted butter over the top layer of dough. Mix the cinnamon and sugar in a small bowl and sprinkle it evenly over the buttered dough.
Bake for 30–35 minutes, or until the top is golden brown and puffed.
Cool for at least 15–20 minutes to allow the filling to set.
While slightly warm or fully cooled, melt the ¼ cup dark chocolate in the microwave (15-second intervals, stirring in between).
Drizzle over the top of the casserole and sprinkle with a small pinch of flaky sea salt.
Slice into squares and serve warm or chilled.