Add onions, carrots, and tomato paste. Cook, stirring often until vegetables have softened and onions are translucent. About 8-10 mins.
Add the garlic, fennel seed, cumin, black pepper, teaspoon of salt & red pepper flakes. Cook, stirring, for one minute.
Pour in canned tomatoes with juice, and add stock.
Add the potatoes and sweet potato. Increase the heat to medium-high and bring the soup to a boil. Partially cover the pot with a lid, then reduce the heat to maintain a low simmer.
Simmer for 20 mins or until the potatoes and other vegetables are tender. Add frozen peas and cook for five more minutes.
Remove the pot from the heat. Stir in the lemon juice and the remaining olive oil.
