Dry roast the foxnuts. Heat a frying pan on the stovetop over low heat. When the pan is hot, add a single layer of foxnuts. Additionally, do not add any oil or cooking spray. Stir frequently with a spatula until they turn crisp and golden. Make sure not to brown them. They can burn easily. It should take about 10 to 12 minutes. However, keep monitoring.
When slightly cool, grind the foxnuts in a spice grinder or a blender coarsely just for a second or 2. Some makhanas need to be intact.
Roast the walnuts, over medium heat for 2 to 5 minutes, until golden. They can brown quickly so watch them. Once golden and fragrant transfer them to a bowl and set aside.
Rinse and chop the cilantro and green chillies finely.
In a large mixing bowl, mix in plain yogurt, milk, sugar, black salt, chaat masala, ground cumin, salt, green chillies, red chili powder, and garam masala.
Add in foxnuts and mix. Finally top off with cilantro and walnuts. Stir and serve the raita if you chill the raita further, it thickens. So you can add some water or milk to thin the raita.
