Heat olive oil in a medium saucepan over medium heat. Add the diced onion and sauté for 2-3 minutes until softened. Stir in the minced garlic and cook for another minute until fragrant.
Add the diced tomatoes, sugar, vinegar, and paprika to the saucepan. Stir well and let the mixture simmer for about 10-15 minutes until the tomatoes break down and combine with the seasonings.
Add more sugar if needed. Season the relish with salt and pepper to taste. Continue to simmer if a thicker consistency is desired. Then, remove from heat and let the relish cool for 1 hour.
Transfer the cooled relish to a jar or serving bowl. Chill for at least 2 hours before serving. Store any leftovers in the refrigerator for up to 1 week.