Place 2. 0 cups (16. 9 oz / 480g) of plain yogurt into a large mixing bowl and whisk it with a fork or wire whisk until it is completely smooth and creamy.
Fold in the 2. 0 cups (8. 8 oz / 250g) of diced mixed vegetables, stirring gently to ensure they are evenly coated in the yogurt.
Combine the 1. 0 tbsp (0. 2 oz / 5g) coriander seeds, 1. 0 tbsp (0. 2 oz / 6g) cumin seeds, and 0. 5 tsp (0. 1 oz / 1. 5g) fennel seeds in a small, dry frying pan. Toast them over low heat, stirring frequently, until they darken a few shades and release a rich, nutty aroma.
Transfer the toasted seeds to a mortar and pestle or a clean coffee mill and crush them into a coarse powder.
Once the spices have cooled to room temperature, stir them into your yogurt and vegetable mixture along with the 1. 0 tsp (0. 2 oz / 6g) salt and 0. 25 tsp (0. 1 oz / 0. 5g) cracked black pepper.
Serve your freshly made Sabji Raita immediately, or cover and refrigerate it for a few hours to let the flavors meld before serving.