Slice a small strip of skin from one side of the eggplant so it lies flat.
Cut 6 more vertical slices up to the stem at about 1/2-inch intervals, leaving the slices attached at the stem to create a fan shape.
Season the slices with 1 teaspoon of salt. Let the eggplant rest for 15-20 minutes to soften and make the slices pliable.
Preheat your oven to 375°F. Line a baking sheet with parchment paper.
In a bowl, mix tomatoes, zucchini, garlic, 1/2 teaspoon oregano, red pepper flakes, and 1/4 teaspoon salt. Drizzle with 1 tablespoon olive oil and toss well. Let sit 5-10 minutes to release the vegetable juices.
In a separate bowl, stir together marinara sauce, the remaining 1/2 teaspoon oregano, and cinnamon.
Combine mozzarella and feta cheese in another bowl and toss to mix.
After the eggplant has softened, pat it dry and place it on the prepared baking sheet. Fan out the slices gently and press down to keep them open.
Brush the cut sides of the eggplant with half of the marinara sauce. Distribute the vegetable mixture evenly between the slices and on top.
Sprinkle half of the cheese mixture over the vegetables and eggplant. Add the reserved vegetable juices to the remaining olive oil and drizzle this mixture over the entire eggplant.
Drizzle with the remaining marinara sauce and top with the rest of the cheese mixture.
Bake for 1 hour to 1 hour 20 minutes, or until the eggplant is tender and the cheese is golden-brown and bubbly.