Heat oil in a medium sauce pot over medium heat for about 2 minutes. Once oil is shimmering, add the onion and tomatoes.
Cook down for 3 minutes, until onions are soft, and the tomatoes are breaking down. Add the kale and garlic, cook for 5 minutes over medium-low, stirring frequently.
Add the sugar, balsamic vinegar, and water. Stir well to incorporate and bring to a simmer. Reduce by 2/3.
Stir in the herbs and cook for another 3 minutes. The mixture should be jammy and thickened. Season with salt and pepper to taste.
Cool completely and store in refrigerator for up to 7 days.
