Finely chop the onion and slice the garlic.
Heat a spoonful of oil in a large, shallow pan and gently sauté the onion garlic. When they are soft, add the chopped (fresh or frozen) vegetables and half a glass of water. Put the lid on and gently cook 5 minutes.
Add the spices, stir for a minute, then add the tomatoes. Put a lid back on and cook for about 10 minutes, until the tomatoes have softened and released their juices.
Now add the peas. Cook for another five minutes (still covered).
Add the spinach, put the lid on and cook for a minute until the spinach has just wilted. Season to taste and stri through.
Lay the fish on top. Squeeze over the lemon juice then season with salt and pepper. Put the lid back on and gently steam for about 5-8 minutes, depending on the thickness of the fish. Be careful not to overcook the fish!
Place the fish on two plates with the stew on the side.