Step 1

Adjust oven rack to middle position and heat oven to 400 degrees. Place potatoes, ⅓ cup oil, minced garlic, and ½ teaspoon salt in 13 by 9-inch baking dish and toss to combine thoroughly. Spread into even layer. Scatter half of onion slices over potatoes. Sprinkle with ½ teaspoon pepper and ½ teaspoon oregano.

Step 2

Scatter bell pepper over surface, followed by remaining onion, sliced garlic, ¼ teaspoon salt, ¼ teaspoon pepper, and remaining ½ teaspoon oregano. Arrange zucchini in single layer. Top with tomato slices, overlapping pieces slightly so they cover entire surface (it should be snug). Pour remaining ⅓ cup oil evenly over tomatoes and sprinkle with remaining ½ teaspoon salt and remaining ¼ teaspoon pepper.

Step 3

Cover dish loosely with aluminum foil, leaving sides open so moisture can escape. Bake for 30 minutes. Remove foil and bake until potatoes can be easily pierced with tip of paring knife and tomatoes have collapsed slightly and started to brown at edges, 40 to 50 minutes. Let cool for at least 20 minutes. Sprinkle parsley over top and serve.