Preheat oven to 325 degrees F. Line an 8-inch square baking pan with foil, allowing the extra foil to hang over the edges of the pan. Lightly coat with non-stick cooking spray; set aside.
Make the Crust: Process the animal crackers in a food processor until finely ground, about 10 seconds. Add the brown sugar and salt and pulse a few times to combine. Drizzle the melted butter over the crumbs and pulse until the crumbs are evenly moistened, about 10 pulses. Press the crumbs evenly into the bottom of the pan. Bake until golden brown, 18 to 20 minutes. Place the pan on a wire rack while you prepare the filling.
Make the Filling: Stir together the cream cheese, lime zest and salt in a medium bowl. Add the sweetened condensed milk and whisk until completely incorporated and no lumps remain. Whisk in the egg yolk, then add the lime juice and whisk gently until incorporated.
Pour the filling into the crust and smooth into an even layer. Bake until the filling set and the edges are beginning to pull away slightly from the sides of the pan, 15 to 20 minutes. Place the pan on a wire rack and cool to room temperature, 1 to 2 hours. Cover with foil and refrigerate until thoroughly chilled, at least 2 hours or overnight.
When ready to serve, run a paring knife around the edges of the pan and lift the bars from the pan using the foil overhangs. Cut into 16 squares and sprinkle with toasted coconut, if desired. Leftovers can be refrigerated in an airtight container for up to 2 days.