Rolled Omelet with Ratatouille Filling

Name: Rolled Omelet with Ratatouille Filling
Ingredients: 1/4 cup olive oil; 1 onion, cut into 3/4-inch dice; Coarse salt and freshly ground pepper; 2 small ripe tomatoes, cored and cut into 1-inch dice; 1 small yellow summer squash or zucchini, cut into 1-inch dice; 1 small eggplant, cut into 1-inch dice; 1/4 cup loosely packed fresh parsley leaves, coarsely chopped; 1/4 cup loosely packed fresh basil leaves, coarsely chopped; 12 large eggs; 2 tablespoons water; 2 tablespoons unsalted butter