Heat olive oil in a pan over medium heat and sauté the onion and garlic until softened.
Add the eggplant and cook for 5 minutes until slightly browned.
Transfer the mixture to the slow cooker.
Add diced tomatoes, olives, capers, red wine vinegar, tomato paste, sugar, salt, black pepper, and red pepper flakes.
Stir to combine.
Cover and cook on low for 4 hours, stirring occasionally.
Stir in fresh basil before serving.
Serve warm or at room temperature with bread or as a side dish.
Notes / Tips / Wine Advice:
Serving Tip:Serve with crusty bread, pasta, or as a topping for grilled meats.Wine Advice:Pairs well with a medium-bodied red wine like Chianti or a dry white wine like Pinot Grigio.