Heat olive oil in a large skillet over medium heat until shimmering.

Add the onion and bell pepper, cooking until softened and fragrant.

Stir in the garlic and cook briefly until aromatic.

Add the ground beef and cook until browned, breaking it into small crumbles as it cooks.

Drain any excess grease from the skillet if necessary.

Mix in the marinara sauce, red wine vinegar, Italian seasoning, crushed red pepper, salt, and black pepper.

Simmer the mixture for several minutes until slightly thickened and flavorful.

Fold in the sliced zucchini and stir until evenly coated with the sauce.

Transfer the mixture to the prepared baking dish and spread it into an even layer.

Sprinkle the cheddar cheese and Italian cheese blend evenly over the top.

Cover loosely with foil and bake until the zucchini begins to soften.

Remove the foil and continue baking until the cheese is melted, bubbly, and lightly golden.

Let the casserole rest for several minutes before serving.

Garnish with fresh basil and serve warm.