Preheat oven to 375 degrees.
Slice both spaghetti squash in half. Scoop out and discard the seeds. Spray cooking spray (or rub 1 teaspoon olive oil) on both the inside and outside of the squash, then place cut side down on a baking sheet. Bake for 40-50 minutes, or until a fork easily pierces the outside skin of the squash.
Meanwhile, add cooking spray (or 2 tsp olive oil) to a skillet over medium high heat. Season chicken breast with salt and pepper, and add to the hot skillet. Cook for 5 minutes, then flip over. Add water or broth to the pan, and continue to cook chicken for approximately 10-20 minutes, until cooked to an internal temperature of 165 degrees. (Cooking time will vary heavily depending on how thick the chicken breasts are – use a thermometer for best results!).
Chop or shred chicken and toss with 1/3 cup BBQ sauce, corn, and black beans.
In each cooked spaghetti squash half, use a fork to scrape the inside of the squash, creating spaghetti-like strands. Mix 1 tbsp sauce into each of the four spaghetti squash bowls (using a total of 4 tbsp between all), lightly coating the squash.
Top spaghetti squash with chicken, corn & black beans. Add cheddar cheese (optional) and cilantro (optional).