Slow Cooker Ratatouille

Name: Slow Cooker Ratatouille
Ingredients: 2 tablespoons olive oil (divided); 1 eggplant (chopped into 1-inch cubes); 2 teaspoons salt (divided); 1 onion (diced); 3 cloves garlic (minced); 3 tablespoons tomato paste; 2 zucchinis (cut into quarters lengthwise and sliced); 1 red bell pepper (cut into 1-inch pieces); 1 orange bell pepper (cut into 1-inch pieces); 3 tomatoes (roughly chopped); 1 tablespoon balsamic vinegar; 1 teaspoon Herbs de Provence ( or Italian seasoning); ½ teaspoon pepper; Fresh basil (chopped (optional)); Red pepper flakes (optional)