Pour 1 cup of boiling water into a medium bowl. Add the lemon gelatin packet and stir constantly for 2 minutes until the gelatin is completely dissolved with no lumps remaining. Checkpoint: The mixture should be clear and smooth.

Add 1 cup of cold water to the gelatin and stir well for 30 seconds. Checkpoint: The mixture should be evenly combined and pale yellow.

Pour the entire can (including juice) of crushed pineapple into the gelatin mixture. Stir gently for 1 minute until the pineapple and gelatin are fully combined. Checkpoint: You should see pineapple pieces evenly distributed throughout.

Place the bowl in the refrigerator for 45–60 minutes. The mixture should look thick and syrupy, similar to pudding, and a spoon should leave a slight impression. If your kitchen is warm, check it at 40 minutes. Checkpoint: You are ready to move on when the gelatin holds its shape when pushed with a spoon.

While the gelatin chills, remove the cream cheese from the refrigerator and let it sit on the counter for 10 minutes to soften.

Place the softened cream cheese in a large mixing bowl. Using an electric mixer on medium speed, beat for 2–3 minutes until the cream cheese is smooth, fluffy, and there are no lumps. Scrape down the bowl halfway through. Checkpoint: The cream cheese should look light and creamy, no visible lumps.

Remove the partially set pineapple-gelatin mixture from the refrigerator. Using a spatula, gently fold it into the cream cheese in 3–4 strokes until just combined. Do not overmix. Checkpoint: The mixture should be swirled together, not completely uniform.

In a separate bowl, make sure your whipped topping is thawed (about 30 minutes at room temperature). Fold half of the whipped topping into the pineapple-cream cheese mixture using 4–5 gentle strokes with a spatula.

Fold in the remaining whipped topping with 4–5 more gentle strokes until the mixture is fluffy and no streaks of white remain. Be very gentle to maintain airiness. Checkpoint: The mixture should look light, fluffy, and pale yellow with no lumps visible.

Gently fold in 1 cup of mini marshmallows using 3–4 strokes. Add 1/2 cup of chopped nuts and fold 2–3 more times until they are evenly distributed. Checkpoint: Marshmallows and nuts should be visible throughout.

Pour the entire mixture into a 9x13-inch baking dish. Smooth the top with a spatula to create an even surface.

Cover the dish loosely with plastic wrap and refrigerate for at least 2 hours, or up to 24 hours. The longer it sits, the better the flavors blend and the firmer the texture becomes. Checkpoint: When you insert a spoon, it should hold its shape and not be soupy.

Just before serving, you may garnish the top with additional shredded coconut (1/4 cup), extra nuts, or a light sprinkle of lemon zest if desired.

Use an ice cream scoop or a large serving spoon to portion the dessert into individual bowls or plates. The dessert should be soft and fluffy, not rubbery.