Heat oil in a large frying pan or skillet over medium-high heat.
Add mustard seeds, and let them crackle.
Add onions and curry leaves. Saute, stirring occasionally, for about 2-3 minutes or until lightly browned.
Add garlic, ginger, and green chilies. Saute, stirring, for about 1 minute or until fragrant.
Add ground turmeric, ground black pepper, red chili powder, and ground coriander. Saute, stirring, for about 30 seconds or until fragrant.
Add tomatoes. Saute, stirring occasionally, for about 2-3 minutes or until the tomatoes break down and turn mushy.
Add vegetables. Stir to combine. Add water. Cook the vegetables, covered, for about 4-5 minutes or until tender.
Add coconut milk. Bring to a gentle simmer. Simmer for about 3 minutes.
Add garam masala and green peas. Simmer for about 2-3 minutes.
Garnish with curry leaves.
Serve with steamed rice.