Soften the onion. Warm the oil in a small saucepan over medium heat. Add the onion and cook 5 to 6 minutes, until soft and translucent.
Add the aromatics. Stir in the garlic and ginger. Cook about 1 minute, just until fragrant.
Toast the tomato paste. Add the tomato paste and stir for 1 to 2 minutes, until it darkens slightly. This is where the colour and depth come from.
Simmer. Add the mashed bananas, vinegar, water, smoked paprika, allspice, cinnamon, cloves, cayenne (if using), and salt. Bring to a gentle simmer and cook 15 minutes, stirring often, until thick.
Blend smooth. Let it cool a few minutes, then blend until silky. Immersion blender right in the pot works well. Add a splash of water if it’s too thick. Taste and adjust the salt, vinegar, or heat.
Cool and store. Let it cool completely, then pour into a clean glass jar. Keep refrigerated.