Heat one tablespoon of coconut oil in a large skillet over medium heat. Add the chopped onion, garlic and grated ginger. Cook until the onions become soft and just start to caramelize, about 7-8 minutes. Add the buckwheat groats and cashews to the skillet and toast them for 2-3 minutes, stirring regularly, until golden brown. Be careful not to burn them.
Add the coriander, cumin, turmeric, smoked paprika and coconut sugar and stir until well combined.
Pour in the coconut milk, soy sauce, sriracha if using and stir in the chopped kale. Cover with the water and bring to a simmer. Cover and cook for about 20 minutes, until the buckwheat groats are soft. You may need to add a little bit more water if too much water has evaporated. Remove from heat and stir in the lemon juice.
Serve as is, or with the sautéed kale (or your favorite greens) on the side.
This curry is best served the same day but will keep for up to three days in the refrigerator.