Preheat the oven to 220°C (430°F), or 200°C if using a fan-assisted oven. Cover a baking tray with parchment paper.
Peel the pumpkin, remove the seeds, and cut the flesh into approximately 3 cm (1.2-inch) cubes. After trimming and cleaning, there should be roughly 1 kg of prepared pumpkin.
Place the pumpkin pieces in a large bowl. Add the extra-virgin olive oil, minced garlic, salt, and black pepper, then toss thoroughly until the cubes are evenly coated.
Arrange the seasoned pumpkin over the lined baking tray in a single, uncrowded layer.
Roast for 20 minutes. Turn the pumpkin pieces over, then return them to the oven for another 7–10 minutes. The pumpkin should develop an appetizing golden color and become tender throughout while still retaining its shape rather than turning mushy.
While the pumpkin cooks, combine the Greek or plain yogurt with the minced garlic, lemon juice, extra-virgin olive oil, salt, and black pepper.
Mix until the sauce is completely smooth and evenly blended.
Leave the yogurt mixture to rest for a minimum of 10 minutes so the garlic, lemon, and seasonings have time to develop throughout the sauce.
While the pumpkin finishes roasting, place a dry skillet over medium-high heat. Do not add oil.
Add the pine nuts, or the chosen substitute nuts, and toast them while stirring frequently. Continue until they are aromatic and lightly browned on both sides.
Transfer the toasted nuts out of the hot skillet immediately to prevent residual heat from scorching them.
Arrange the hot or warm roasted pumpkin in a generous mound on a serving plate.
Spoon or drizzle the prepared yogurt sauce liberally over the roasted pumpkin. A small additional drizzle of olive oil may be added if desired.
Finish with the toasted pine nuts, chopped cilantro or parsley, and a light sprinkling of sumac, paprika, or the selected alternative spice.
Serve immediately while warm, or allow the roasted pumpkin to cool before assembling if the dish is intended to be enjoyed at room temperature.