Preheat a soup pot to medium heat with the olive oil. Add the onion with a sprinkle of salt and pepper and cook for 3 minutes. Add the potato with more salt and stir to coat in the olive oil - cook for 3 minutes more. Add the garlic to the vegetables and cook for 1-2 minutes, just until fragrant. Sprinkle the flour over the potato mixture and stir it into the vegetables.

Add the frozen vegetables to the pot, and squish the tomatoes into the pot with your hands. Add the stock, and stir the soup to combine everything and pick up any bits from the bottom of the pan. Increase the heat to medium-high and cover the soup to bring it to a boil. When the soup boils, reduce the heat to medium-low and simmer the soup for 20 - 30 minutes until the potatoes and other vegetables are tender. Taste, and add more salt or pepper to the soup as desired.

To serve, add a handful of spinach leaves to the bottom of a bowl. Top with soup and add any desired toppings.