Preheat the oven to 400°F (200°C). Line a baking tray with parchment paper.

Thinly shave the zucchini lengthwise using a mandoline or vegetable peeler. Pat the slices thoroughly dry with paper towels.

Sprinkle half the shredded cheese over the parchment in a thin rectangle. Arrange the zucchini slices in slightly overlapping rows to form a rectangle over the cheese. Sprinkle the remaining cheese over the zucchini and season with garlic powder and black pepper.

Bake for 18 to 20 minutes, until the cheese is golden and crisp around the edges. Watch carefully towards the end to prevent burning.

Cover the eggs with water in a pot. Bring to a boil for 8 minutes. Drain the water and run cold water over the eggs. Once able to handle peel the shells off the eggs and chop.

Combine the drained tuna, chopped hard-boiled eggs, scallions, dill, red onion, and diced pickles in a bowl.

Add the mayonnaise, Dijon mustard, and lemon juice. Season with black pepper and mix thoroughly.

Remove the zucchini cheese base from the oven and allow it to cool slightly so it becomes easier to handle.

Spread the tuna salad evenly over the base, leaving a small border around the edges. Arrange the tomato slices and optional jalapeño over the filling.

Carefully roll the zucchini base tightly from the bottom, pressing gently to keep the filling compact. Slice in half with a sharp knife.

Combine the sparkling water, lemon, and chia seeds. Let stand for 5 minutes, then stir again. Add ice before serving if preferred.