Heat 3 tablespoons oil in a skillet over medium heat; add mustard seeds and cook until they crackle, 1 to 2 minutes. Add onion and cumin seeds; cook and stir until onion is translucent, 5 to 10 minutes. Add ginger-garlic paste, chili powder, and turmeric; cook and stir until fragrant, 1 to 2 minutes.
Mix broccoli into onion mixture; cook and stir until tender, 8 to 10 minutes. Add water and salt; cook and stir for 1 minute. Stir gram flour into broccoli mixture; cook, stirring constantly, until broccoli is coated and doesn't stick to skillet, adding more flour if needed, 5 to 8 minutes. Drizzle 1 teaspoon oil over junka to serve.