Add the olive oil and butter to a pot over low heat. Saute the diced onion for about 10 minutes over low heat until the onion becomes transparent.
Sprinkle the flour over the onion, and cook for an additional 5 minutes stirring occasionally.
Next, add the vegetable broth and potatoes to the pot and bring to a boil. Reduce heat to medium, cover the pot with a lid, and allow it to simmer until the potatoes are tender, for about 10 minutes.
Add the corn, bell peppers, salt, pepper and half and half. Continue to simmer the chowder over low heat for about 10 minutes, stirring frequently.
Ladle the soup into a serving bowl, and garnish with the tomato and basil.