To make pickled onions, whisk together first four ingredients in a bowl. Pour over sliced red onions and leave for minimum one hour. You can place onions and liquid in a sterilised jar and into the fridge if you are pickling for more than an hour.
Preheat oven to 180°C. Line an oven tray with baking paper. Scoop out the seeds of your pumpkin. Leave skin on. Cut into one centimetre slices and place on prepared tray. Drizzle with olive oil and salt and toss to coat. Roast for 40 minutes until soft. Once cooked, remove and set aside to cool.
Meanwhile, place pistachios into a dry fry pan over a medium to high heat. Toast for five minutes until fragrant. Set aside to cool before roughly chopping.
To make the dressing: whisk all ingredients in a bowl. Add water slowly, whisking in between each addition until dressing reaches a pourable consistency.
To assemble salad: in a large bowl (or four individual plates), layer baby spinach with roasted and cooled pumpkin, chickpeas, chopped pistachios, crumbled feta and pickled onions. Drizzle with tahini dressing and serve immediately.
Notes
Some swaps you could make:
Butternut pumpkin can replace Kent pumpkin and you can remove the skin if you'd prefer, although roasting makes pumpkin skin lovely and soft.
Substitute pistachios with chopped almonds, pine nuts or pumpkin seeds.
You could use goats cheese in place of feta, or some pan fried haloumi.
You do not need to pickle the onions if you don't have the time, however I do highly recommend this as it adds another flavour profile to the dish.
Honey can be subbed in for the maple syrup if you'd prefer.