Cover the cashews with water and let them soak for a few (2-3) hours (or overnight in the fridge). Then rinse and drain.
Toss the cauliflower florets in oil, mild curry powder, and salt. Add them to a baking tray lined with parchment paper. Bake them for 15-20 minutes at 400°F/200°C until soft and slightly brown on the edges.
Add the cashews, clean water, and salt into a blender. Blend until completely smooth.
In a small pot over medium to high heat, cook the diced onion and minced ginger until soft.
Reduce the heat, then add the diced tomatoes and cashew sauce. Stir and add more salt to taste. If it's too thick, you can also thin it out with water and let it cook until warm.
Add the roasted cauliflower into the curry, give it a quick stir and serve with basmati rice and naan!