Add turmeric, cumin, coriander, paprika, chili powder, and salt to the skillet. Sauté for 1–2 minutes until aromatic. Then, stir in grated garlic, grated ginger, cashews (if using), diced tomatoes, and 1/3 cup water. Simmer for 10–15 minutes, stirring occasionally, until the sauce thickens and the flavors come together.