Heat the oil in a medium saucepan over medium heat. Add the onion and cook until soft and translucent, about 5-7 minutes. Add the garlic and tomato paste and stir to combine, cooking 2-3 minutes until the tomato paste breaks down and melts into the onion and garlic.
Add the mashed banana and stir until they pick up the reddish-orange hue from the Annatto Oil and tomato paste. Pour in the vinegar and water, stirring to scrape up any browned bits from the bottom of the pan.
Add the brown sugar, black pepper, ground clove, salt, and soy sauce and stir to combine. Drop the bay leaf into the pan and bring mixture to a boil. Reduce heat to low and simmer, partially covered, for 20-30 minutes. Remove from heat and discard the bay leaf.
Once cool enough, pour mixture into food processor or blender and puree until smooth (I only pureed about 2/3 of the mixture, adding back the 1/3 that wasn't pureed for a bit of texture). If the banana ketchup is too thick, it can be watered down with additional water. Taste for seasoning and add more sugar if a sweeter ketchup is desired.
Store in an airtight container in the refrigerator for 2-3 weeks.
Optional: For a spicier version, add 1-2 chopped Thai chili peppers or 1 small jalapeno pepper with the onions and sautee. Continue with the rest of the recipe as directed.
Note: You can vegetable oil if you don't want to make Annatto Oil. To make Annatto Oil - combine 2 cups of canola oil, 1/2 cup annatto seeds, 2 tsps whole black peppercorns, and 1 bay leaf in a large saucepan over moderately high heat. Warm the oil until it just begins to bubble. Remove from the heat and set aside for 1-2 hours to steep. Strain through a fine mesh strainer, discarding the solids. Store in an airtight container in the refrigerator for 3-4 weeks.