Oven should be preheated to 425°F (220°C) and the large baking sheet should be lined with parchment paper.
Clean the cauliflower and dry it well. Cut it up into bite-sized pieces of even size.
Place the cauliflower florets into a big mixing bowl.
Spread the olive oil on the cauliflower and then add the curry powder, turmeric, cumin, garlic powder, paprika, salt, black pepper and, if desired, the red pepper flakes.
Mix the cauliflower well using your hands or a large spoon until all the florets are evenly covered with the oil and the spices.
Place the cauliflower on the already prepared baking sheet in a single layer, making sure to leave some space between the pieces.
Roast for 15 minutes and then carefully toss or turn the florets so that they brown evenly.
Keep roasting for an additional 10 to 15 minutes until the cauliflower is tender in the centre and has a golden brown colour with crispy roasted edges.
Take the cauliflower out of the oven and let it cool for 2 to 3 minutes.
Add some fresh lemon juice and toss in chopped cilantro.
Toss it gently one more time and then serve it while it's warm.