For the enchilada sauce: In a medium saucepan, spray oil and sauté garlic. Add chipotle chiles, chili powder, cumin, chicken broth, tomato sauce, salt and pepper. Bring to a boil. Reduce the heat to low and simmer for 5-10 minutes. Set aside until ready to use.
For the Zucchini Boats: Bring a large pot of water to boil.
Preheat oven to 400°. Cut zucchini in half lengthwise and using a small spoon or melon baller, scoop out flesh, leaving 1/4″ thick. Chop the scooped out flesh of the zucchini in small pieces and set aside.
Drop the zucchini halves in boiling water and cook 1 minute; remove from water.
In a large saute pan, heat oil and add onion, garlic and bell pepper. Cook on medium-low heat for about 2-3 minutes, until onions are translucent. Add chopped zucchini and cilantro; season with salt and pepper and cook about 4 minutes. Add the cumin, oregano, chili powder, water, and tomato paste and cook a few more minutes, then add in chicken; mix and cook 3 more minutes.
Place 1/4 cup of the enchilada sauce on the bottom of a large (or 2 small) baking dish, and place zucchini halves cut side up. Using a spoon, fill each hollowed zucchini with 1/3 cup chicken mixture, pressing firmly.
Top each with 2 tablespoons of enchilada sauce, and 1 1/2 tablespoons each of shredded cheese.
Cover with foil and bake 35 minutes until cheese is melted and zucchini is cooked through.
Top with scallions and cilantro for garnish and serve with low fat sour cream if desired.