Heat a medium-sized pan on medium heat. Add chopped onion to the pan. Season with salt and pepper. The salt will help draw the moisture out of the onion, which helps with the sweating. Allow to sweat for 5 minutes. Add garlic and chilli flakes.
Add the leeks to the onion and toss everything together. Season with salt and pepper. Add the red pepper to the pot, along with rest of the veggies. Stir everything together and allow to cook for 5 minutes. Add the cabbage, potatoes, tomatoes and water. Cover and simmer for 15 minutes.
Check on the potatoes. The potatoes should be fork tender. If not, ensure that there is sufficient liquid in the pot for it to keep simmering gently, without burning. Add in about half a cup of water at a time to the pot, if needed.
Once everything is tender and cooked, remove from heat, check for seasoning and sprinkle with dill and parsley before serving.