Heat 1 tablespoon olive oil in a large skillet over medium heat. Once it’s hot, add the onion and garlic, cooking for 3 to 5 minutes until fragrant, shiny, and translucent.
Add the tomato paste in the middle of the pan and let it sit sizzling for 30 seconds. Mix it in with the onions and garlic and cook for 30 more seconds to 1 minute, until it starts smelling caramelized.
Add the fire roasted diced tomatoes, mix, and let simmer for 5 minutes.
Reduce heat to medium-low.
Add 1 sardine and 1 tablespoon Thai caramel sauce (or 1/2 tablespoon coconut or palm sugar + 1/2 tablespoon fish sauce). Break apart the sardine and stir together, cooking for 3 to 5 minutes.
Reduce heat to low. Use an immersion blender to the get the sauce more smooth or to the consistency you prefer.
Add the oregano, salt, and pepper and stir. Turn off heat and set aside.