Preheat the oven to 400°F/200°C, and line a large baking sheet (or two small) with parchment paper or a silicone liner.
Toss the eggplant, bell pepper, and onions with olive oil and 1/4 teaspoon of salt, and roast for about 30 minutes until the vegetables are cooked through, and the eggplant is soft and golden.
While the vegetables are cooking, make the dressing. Throw all of the dressing ingredients into your blender, and blast on high for 30 to 60 seconds until the ingredients are pulverized and the mixture is emulsified.
In a large bowl, add the roasted vegetables with the romaine, mint, chives, and watermelon seeds. Add the dressing, and toss gently until evenly coated. Serve half the salad, and transfer the remaining salad to a sealed container in the fridge for tomorrow.