Slice and salt the zucchini. Cut the zucchini in half and then stand each piece on end. Cut into even slabs from top to bottom. Salt each piece liberally to draw out the moisture and place in a strainer or on a plate for 10-15 minutes. Drain off any water that collects and dab dry with a towel if necessary.
3 medium zucchini, salt and pepper
Slice the rest of the veggies. Cut the outer flesh off the tomato to remove the seeds and the core. Set the flesh aside for the casserole and compost the core. Slice the peppers and onions thin but evenly and set aside for layering.
1 large bell pepper, 4 medium roma tomatoes, 1 medium onion
Prepare the cheese mixture. Shred the cheese and add to a large bowl. Season with garlic powder, Italian seasoning, salt and black pepper. Combine well and set aside for layering.
2 cups cheese, ½ teaspoon garlic powder, 1 teaspoon Italian seasoning, salt and pepper
Layer the casserole. Start with a layer of zucchini in the casserole dish for an even base. Layer in the sliced tomatoes, bell pepper, and onions. After one layer of each, add a layer of cheese in the middle leaving at least half for the topping. Continue layering until all the veggies are used up or the dish is full. Finish with a thick layer of the cheese mixture.
Bake for 35-40 minutes. Bake in a 400°F [205°C] oven for 35-40 minutes until the vegetables are tender and the cheese topping is starting to brown.
Rest and serve. Remove the casserole from the oven and allow it to rest and cool for around 10 minutes. Use a large spoon or spatula to scoop out servings and enjoy!