Preheat the Oven: Preheat your oven to 180°C (350°F). Grease and line an 8-inch square baking dish with parchment paper or lightly oil it.
Prepare the Vegetables: Finely chop the red onion and roughly chop the roasted pepper, sun-dried tomatoes, and black olives. Grate the courgette (zucchini) and place it in a clean kitchen towel. Squeeze out as much moisture as possible to prevent the bake from becoming too wet.
Combine the Dry Ingredients: In a large mixing bowl, combine the oats, chopped nuts, mixed seeds, mixed dried herbs, garlic granules (or fresh garlic), salt, and black pepper.
Add the Vegetables and Feta: Stir in the chopped red onion, courgette, roasted peppers, sun-dried tomatoes, black olives, and crumbled feta cheese.
Incorporate the Wet Ingredients: In a separate bowl, beat the eggs and then add the melted butter. Pour this mixture over the oat and vegetable mixture. Add the finely chopped fresh herbs. Mix everything together until well combined.
Transfer to Baking Dish: Pour the mixture into the prepared baking dish, spreading it out evenly and pressing down gently to compact it. Drizzle a little olive oil over the top to help it crisp up as it bakes.
Bake: Place the dish in the preheated oven and bake for 35-40 minutes, or until the top is golden and the bake is set. A toothpick inserted into the center should come out clean.
Cool and Serve: Allow the oat bake to cool in the dish for at least 10 minutes before slicing. This will help it set and make it easier to cut into portions. Serve warm or at room temperature, garnished with extra fresh herbs if desired.