Prepare the Buckwheat:
In a medium saucepan, bring the buckwheat groats, water, olive oil, and salt to a boil. Reduce heat to a simmer and cook for about 20 minutes, or until tender. Drain any excess water and set aside.
Preheat the Oven and Prepare the Baking Tray:
While the buckwheat is cooking, preheat your oven to 375°F (190°C). Line a baking tray with parchment paper and set aside.
Prepare the Butternut Squash:
Slice the butternut squash into half-moon shapes and arrange them on the prepared baking tray. In a small bowl, mix the sumac, smoked paprika, cumin, cayenne pepper, Celtic salt, coriander, cinnamon, and olive oil. Brush each squash slice generously with the spice mixture on both sides. Roast in the oven for 35-40 minutes, until tender and golden.
Toast the Pine Nuts:
About 10 minutes before the squash is ready, add pine nuts to a flat baking tray and place in the oven. Toast until golden brown (watch closely to prevent burning), or toast in a skillet on the stovetop over medium heat. Set aside.
Prepare the Hummus:
In a food processor, combine butterbeans, tahini, lemon juice, cumin, salt, cayenne, and olive oil. Blend until smooth, adding water a spoonful at a time to reach a creamy consistency.
Assemble the Salad:
In a large bowl, combine the cooked buckwheat, toasted pine nuts, pineapple guava slices, bell pepper, red cabbage, sun-dried tomatoes, and fresh herbs. Add lemon juice, salt, and pepper to taste. Toss to coat and refrigerate until ready to serve.
Serve the Dish:
To plate, spread a generous amount of hummus (about 1/3 cup) on each plate in a circular motion. Arrange the roasted butternut squash slices over the hummus, and spoon the buckwheat salad on top.
Enjoy:
Serve immediately, or keep each component stored separately in the refrigerator and assemble just before serving.