Preheat the oven to 350 degrees F (175 degrees C). Lightly grease a 2 quart casserole dish.
In a medium bowl, toss together the carrots, bell pepper, onion, garlic, and spinach. In a separate bowl, blend together the Gouda cheese, mozzarella cheese, and sharp Cheddar cheese. Set aside.
Place two layers of sliced potatoes in the bottom of the prepared casserole dish. Season the potatoes with a little salt and pepper. Top with a layer of the spinach mixture, and pour about 1/2 cup of sauce over all. Sprinkle with some of the cheese blend. Repeat layering with remaining potatoes, vegetables, sauce and cheese, ending with cheese on the top.
Bake covered for 35 minutes in the preheated oven. Remove the lid, and bake for 10 more minutes until the top is browned.