Preheat the oven to 220°C/425°F and line a rimmed baking sheet with parchment. Heating the oven hot from the start helps the sweet potato slices crisp at the edges while softening in the middle—important for a toast-like texture.

Wash and dry the sweet potatoes. Using a sharp chef’s knife or mandoline, slice lengthwise into 8–10 mm (about 1/3–3/8 inch) slabs. Uniform thickness ensures even cooking so some slices don’t burn while others remain underdone.

Place the sweet potato slices in a single layer on the prepared sheet. Brush both sides lightly with half the olive oil (about 1/2 tbsp) and season with a pinch of sea salt and a few grinds of black pepper. Rubbing oil on both sides promotes browning and creates a crisp exterior.

Roast on the middle rack for 12 minutes, then flip each slice, brush with the remaining oil, and roast another 8–10 minutes until golden at the edges and tender when pierced with a knife. Flipping exposes both sides to dry heat so you get a caramelized surface rather than a steamed one.

While the sweet potatoes roast, prepare the avocado: halve, remove the pit, and scoop the flesh into a bowl. Mash lightly with a fork so it’s still a little chunky (or leave slices if you prefer). Add the lemon zest, a pinch of salt and pepper — the lemon brightens the avocado and prevents rapid browning.

Warm the prosciutto briefly: in a dry skillet over medium-high heat, lay the slices in a single layer and cook 20–30 seconds per side until slightly translucent and just starting to crisp at the edges. This concentrates flavor and changes prosciutto from floppy to slightly crisp without making it hard.

When the sweet potato slices are ready, transfer them to a cooling rack or plate. Taste one and adjust salt if needed — sweet potato can taste blander after cooking, and a little salt brings out the caramelized sugars.

Assemble on a serving platter: spread about 2–3 tablespoons of mashed avocado on each sweet potato toast (or thickness to your liking). Top each with folded prosciutto (2–3 slices per person total, distributed across the toasts) and a small handful of arugula.

Finish with a light drizzle of the remaining olive oil if any, or another 1/2 tsp, extra lemon zest over the top, and a crack of black pepper. The final lemon zest and oil marry the textures — silky avocado, salty prosciutto and crisp-tender potato.

Serve immediately so the sweet potato toasts remain crisp at the edges. If left too long, the avocado will hydrate the potato and soften it — serve hot or warm for the best texture contrast.