1. In a large skillet, sauté onion over medium heat with vegetable stock, stirring frequently, until onion becomes translucent. Stir in garlic, ginger, turmeric, coriander, cumin, and garam masala. Cook for 2 minutes.
2. Stir in diced tomatoes, tomato paste, salt, and cayenne pepper, and cook for 3–4 minutes. Stir in vegetables, coconut milk, and lemon juice. Cover and cook for 10–12 minutes on low heat.