Start with getting a big pot on the stove on a low to medium heat. Drizzle in a generous amount of olive oil. Once warm, add the onion, salt, and garlic. Sautée until softened.
Add the peppers and turn up the heat a little. Once they're starting to cook down, add the marmite and the sundried tomatoes. I like adding some of the oil from the sundried tomatoes too.
Throw in the sweet potato and potatoes, a bit of black pepper, the kombu leaf, the bay leaves, the puréed tomato, and the water.
Stir well and let simmer for an hour. After an hour, you can take this off the heat. Let rest until you're read to serve the minestrone.