Place eggplant in a colander. Season generously with salt; toss to coat evenly. Let drain for 30 minutes. Rinse eggplant, and pat dry with paper towels.
Toss tomatoes with 2 tablespoons oil, the thyme, and oregano in a large bowl. Season with salt and pepper.
Preheat oven to 450 degrees. Toss together eggplant, onion, garlic, and 2 tablespoons oil in a large bowl. Season with salt and pepper. Spread vegetables out into an even layer on a rimmed baking sheet. Toss zucchini and bell peppers in bowl with remaining 2 tablespoons oil. Season with salt and pepper. Spread out into an even layer on another rimmed baking sheet. Roast vegetables, rotating sheets once, until golden and tender, about 45 minutes. Immediately transfer cooked vegetables to tomato-herb mixture. Stir to combine. Let cool.
Brush slices of bread with oil. Place on a rimmed baking sheet, and lightly toast in oven, about 2 minutes.
Fill a large, shallow saucepan with 4 inches of water, and bring to a boil. Reduce heat to medium. When water is barely simmering, break 1 egg into a small bowl. Gently tip bowl, carefully sliding egg into water. Repeat with remaining eggs. Cook until whites are set but yolks are soft, 3 to 4 minutes. Using a slotted spoon, transfer eggs to a paper-towel-lined plate to drain.
Spoon ratatouille over bread slices. Top each with a poached egg, and season with salt and pepper. Garnish with thyme.