Step 1Heat the oven to 400 degrees.
Step 2In a large bowl, toss the cauliflower with the canola oil and season with one-fourth teaspoon salt and a pinch of pepper, or to taste.
Step 3Place the cauliflower in a roasting pan (reserve the bowl) and roast until the cauliflower is a deep brown and tender throughout when pierced with a knife, 20 to 25 minutes, tossing every few minutes for even coloring and cooking. Remove the cauliflower from the oven and reduce the oven temperature to 250 degrees.
Step 4While the cauliflower is roasting, cook the rice: In a large saucepan, add the water and a generous pinch of salt and bring to a boil over high heat. Stir in the rice and chili flakes and reduce the heat to a gentle simmer. Cook the rice just until tender, about 15 minutes. Drain the rice well, then spread the rice in a thin shallow layer in a large baking dish.
Step 5Place the rice in the oven to dry out for 5 minutes. Remove, then stir in the olive oil. Taste and adjust seasoning as desired with salt and pepper.
Step 6Place the cauliflower back in the bowl and toss with the curry powder. Taste and season, if desired, with additional salt and pepper.
Step 7Gently stir in the warmed rice and butter, tossing until the butter is melted and evenly coats the rice and cauliflower. Stir in the green onions and serve immediately.