Peel and finely chop the onion. Trim, peel and finely chop the carrots. Peel and grate or crush the garlic. Peel the ginger. Finely grate it.
Warm a frying pan over a medium heat. Add 1 tsp oil to the warmed pan. Tip in the onion and carrots. Cook for 3-4 mins till the onion is just soft. Add the garlic, ginger, 2 tsp garam masala and 1 tsp turmeric. Season with salt and pepper. Cook and stir for 1 min.
Pour in the chopped tomatoes. Half fill the tin with cold water (around 200ml). Add this to the pan. Stir and bring to a simmer. Drain and rinse the chickpeas. Add to the pan. Cover and cook for 10 mins.
After 10 mins, carefully place the pollock fillets in the pan. Replace the lid. Cook for 15 mins. While the pollock cooks, pick the leaves from the coriander. Finely chop the stalks.
Check the pollock is cooked by carefully inserting a sharp knife. The flesh should be flaky and opaque. If it's not, cover the pan again and cook for another 2 mins.
When the fish is cooked, gently lift it out onto a plate. Cover with foil. Tip the baby spinach and coriander stalks into the channa masala. Stir for 2 mins till the spinach is wilted. Juice in half the lime. Taste and adjust the seasoning.
Serve the pollock with the channa masala. Scatter over the coriander leaves and serve with the remaining lime, cut into wedges, for squeezing.