Peel seed, and cut the cucumber into 1/2-inch dice. Set aside. Heat 1 tablespoon of the ghee in a small saute pan over medium heat. Add the mustard seeds and saute for about 3 minutes, or until the seeds begin to pop. Remove immediately from the heat. Combine yogurt and buttermilk in a mixing bowl. Whisk in the mustard seeds and ghee. Fold in 1/2 cup of the onion and the reserved cucumber. Taste and adjust the seasoning with salt. Cover and refrigerate the raita until ready to use. Put the carrots and beans in a medium saucepan filled with rapidly boiling water and blanch for 30 seconds. Drain well and refresh under cold running water. Pat dry and set aside. Put the remaining 1/4 cup of ghee in a large saucepan over medium heat. Add the cayenne chile, garlic, ginger, and the remaining onion and saute for about 4 minutes, or until golden brown. Add the lime juice. Stir in the peas and the reserved carrots and beans and saute for 5 minutes. Stir in the saffron, cumin, garam masala, and turmeric and saute for 1 minute. Add the rice and continue to saute for an 5 additional minutes. Stir in the cashews and serve with a bowl of tempered onion-cucumber raita on the side.