Roast the pumpkin to concentrate its sugars and remove excess water. Preheat oven to 200°C (400°F). Tear the pumpkin flesh into 2–3 cm chunks, toss with 2 tbsp olive oil and a pinch of salt, spread on a rimmed baking sheet in a single layer. Roast 35–40 minutes until deeply golden at the edges and a knife slides in easily. Why: roasting caramelizes natural sugars and reduces moisture, giving a richer, more pumpkin-forward flavor than boiling or steaming.

Make the pumpkin purée: when the pumpkin is soft and cool enough to handle, scrape flesh into a blender or food processor with 40 g maple syrup, 200 g coconut milk, 1 tsp cinnamon, 1/2 tsp ginger, 1/4 tsp cardamom, 1/4 tsp sea salt and 1 tsp vanilla. Puree until perfectly smooth (about 1–2 minutes). Taste and adjust sweetness/spice. Why: blending while warm helps the mixture become silkier and integrates the coconut milk evenly; the spices and maple balance pumpkin's earthiness.

Cool the purée: transfer the purée to a bowl and chill in the fridge while you prepare the other components (or set in an ice bath for 10–15 minutes). Cooling keeps the aquafaba from collapsing when you fold it in later.

Whip the aquafaba: in a clean, grease-free bowl, add 120 g aquafaba, 40 g granulated sugar and 1/8 tsp cream of tartar. Whisk with an electric mixer on medium-high until stiff, glossy peaks form (7–10 minutes). Why: aquafaba traps air like egg whites; the sugar stabilizes the foam and cream of tartar lowers pH to help firm the peaks — this gives the mousse its airy lift without dairy or eggs.

Fold aquafaba into pumpkin purée: take about one-quarter of the whipped aquafaba and whisk vigorously into the chilled pumpkin purée to loosen it (this 'tempers' the base). Gently fold in the remaining aquafaba with a silicone spatula in 2–3 additions, using wide strokes to preserve the foam. Why: tempering avoids deflating all the whipped aquafaba at once; gentle folding keeps the texture airy while giving structure.

Make the ginger-almond oat crumble (crunch): preheat oven to 175°C (350°F). In a bowl combine 60 g rolled oats, 40 g almond flour, 30 g brown sugar, 1/2 tsp ground ginger, 1/4 tsp cardamom and 40 g melted coconut oil. Mix until clumps form. Spread thinly on parchment and bake 12–14 minutes, shaking the tray halfway, until golden and crisp. Break into rough crumbs. Why: the warm spice and toasted almond-oat crunch give necessary textural contrast to the mousse and lends a toasty, nutty note.

Make candied pecans: toss 90 g pecans with 20 g maple syrup and a pinch of sea salt on a small baking sheet. Roast at 175°C (350°F) for 10–12 minutes until syrup is bubbling and nuts are toasted; remove and separate with a fork so they don't clump. Cool — they'll crisp as they cool. Why: the candied nuts add caramelized sweetness, crunch and a toasty flavor that pairs with pumpkin spices.

Toast pumpkin seeds: in a small dry skillet over medium heat, toast 30 g pumpkin seeds until they pop and smell nutty, 3–4 minutes. Shake frequently. Remove from heat to cool. Why: toasted seeds lend a clean, pumpkin-y crunch and visual contrast on the finished dessert.

Assemble the mousse: spoon or pipe the pumpkin mousse into six dessert glasses or bowls (about 140–160 g per serving). Sprinkle a layer of ginger-almond crumble, add a few candied pecans, and finish with toasted pumpkin seeds and a small drizzle of the reserved maple (about 1–2 tsp per serving). Finish with a little lemon zest if using. Why: layering keeps textures separate so each bite has silky mousse, crunchy crumble, and candied nuts.

Chill to set: cover and refrigerate the assembled desserts for at least 1–2 hours so the mousse firms slightly and the flavors meld. Why: chilling allows the aquafaba-stabilized mousse to relax and set, improving mouthfeel and flavor integration.

Serve and store: serve cold or slightly chilled. Leftovers can be refrigerated for up to 3 days (nuts will soften over time). Why: serving chilled heightens the mousse's creaminess, and note that aquafaba foams maintain structure best when cold.