Set your oven to preheat to 450 degrees Fahrenheit.
Create steaks: Slice a cauliflower in half, cutting vertically down through the stem. Then slice as many 1-inch wide steaks as you can from each half. You should get two to three per cauliflower. Snap the rest into little florets. Repeat with remaining cauliflower.
Line a couple of baking sheets with parchment paper or foil. Use cooking spray or brush with a little olive oil to keep the cauliflower from sticking. Place steaks on one baking sheet, florets on the other.
In a small bowl, whisk together oil, cumin, coriander and amchur. Season generously with salt and pepper. Brush over steaks with pastry brush; drizzle over florets and toss to coat.
Pop into the oven and roast for 20 minutes until tender and crisped around the edges.
In another small bowl, whisk yogurt with lime zest, a splash of extra virgin olive oil (about a teaspoon), salt and pepper and a squeeze of lime (as much as you like, depending on how tart you like things!).
Serve steaks with a dollop of yogurt on the side.