Scrape out the seeds from the pumpkin and cut the pumpkin into slices. Peel and then cut the pumpkin slices into medium-size pieces.
Roughly chop the tomato.
On a medium burner, heat oil in a pressure cooker on a medium flame (refer to notes for cooking in a pot).
Add the cumin seeds, mustard seeds, fennel seeds, fenugreek seeds and finally onion seeds (kalonji). Add the spices in the order mentioned because the fennel seeds, fenugreek seeds and onion seeds should not be cooked for long as they can burn easily and turn bitter. Sizzle for 5 seconds, taking care not to burn the seeds. Reduce the flame to low if needed.
Add the chopped pumpkin, tomato, salt, chilli powder and sugar.
Add the measured water.
Close the lid and cook on high flame till the first whistle (Some pressure cookers whistle while releasing steam. If you have one that doesn’t whistle, then cook as per the required settings). After the first whistle, immediately reduce the flame to low and switch off the gas after 5 minutes. Let the steam release on its own and then open the lid.
Blend till smooth using a stick blender. Add hot water if needed to adjust the consistency. Taste and add seasoning if required. The seeds do not blend completely, so if preferred, strain the soup.
Garnish with freshly chopped herbs, cream or pumpkin seeds.
Serve hot with your choice of bread.