Ratatouille Stuffed Bread

Name: Ratatouille Stuffed Bread
Ingredients: 3 Tbsp olive oil; 1/2 large spanish onion, peeled and sliced; 1 Tbsp kosher salt; 1 Tbsp fresh ground black pepper; 1 small/medium eggplant, sliced into rounds about ½ inch thick; 1 zucchini, trimmed and sliced into coins; 1 yellow squash, trimmed and sliced into coins; 1 pt cherry tomatoes, halved; 1 small red pepper, cored, seeded, and sliced; 1 pt button mushroons, roughly chopped; 1 clove large garlic, peeled and crushed; 1/2 tsp granulated sugar; 1/2 c tomato sauce; 1 Tbsp shredded fresh basil; 1 loaf - frozen bread dough; 1 1/2 c shredded mozzarella; 2 Tbsp butter, melted