Preheat oven to 350 ̊ F. Spray an ovenproof skillet with cooking spray, add 2 teaspoons oil and tilt pan to coat. Add cumin, turmeric, and curry powder and heat over medium-high heat, 30 seconds.
Reduce heat to medium-low. Add remaining oil and onion and stir gently to coat. Cook, stirring frequently, 5 minutes, or until onion softens. If pan becomes too dry, spray with little more cooking oil spray.
Mix water, lemon juice, salt, and pepper. Add cauliflower to pan and stir gently to coat. Add lemon juice mixture and stir to combine. Cover, place pan in oven and roast about 25 minutes, or until cauliflower is softens.