Mix flour, coriander, cumin, chile pepper, mustard powder, turmeric, and salt together in a bowl. Mix in water until a paste forms. Stir in skim milk and yogurt.
Heat oil in a nonstick pot over medium heat. Add cumin seeds; heat until fragrant, 1 to 2 minutes. Add spice paste; heat for 1 minute. Add cauliflower to the pot and toss with spice paste until completely coated. Cover and cook cauliflower over medium-low heat, stirring several times to coat and prevent burning, until tender, 10 to 12 minutes.
Stir lemon juice into the cauliflower just before serving.