Wash the zucchini and yellow squash and them in half, lengthwise. Cut the zucchini and yellow squash in half lengthwise again and cut out the seeds. Cut them once more by half, lengthwise. Dice the zucchini and yellow squash into small cube pieces.
In a shallow bowl, place a clean paper towel on the bottom and transfer the cut zucchini and yellow squash on top. Sprinkle about 1/2 teaspoon of salt over them. Gently toss together so the salt can cover the zucchini and yellow squash evenly. Let them salt while you prepare other vegetables.
Heat a tablespoon of oil in a large skillet. Add the onion and bell pepper. Cook until onion becomes translucent, about 3-4 minutes.
Add the chopped tomato to the mixture and continue to cook for couple more minutes.
Using the paper towel, pat the zucchini and yellow squash dry. Add the zucchini and yellow squash to the mixture.
Add the black bean, cumin, chili powder, and black pepper to the mixture and stir until everything is well mixed. Add about a pinch of salt to the mixture.
Remove the mixture from heat.
Add about 2/3 cup of red enchilada sauce and 1/2 cup of cheese to the vegetable mixture. Mix well.
Preheat the oven to 400F.
While the oven is preheating, assemble the enchiladas.
Place about 1/2 cup of red enchilada sauce on the bottom of a 9 x 9 inches baking pan. Spread the sauce so the bottom is completely covered with the sauce.
Place about 1/2 cup of the vegetable mixture on top of tortillas and roll them tightly. Transfer to the baking dish, the seam side down. Repeat until all the vegetable mixture is used up.
Pour the rest of the enchilada sauce on top of the assembled enchiladas and sprinkle with the rest of the cheese.
Bake for 16-18 minutes. Garnish with fresh avocado, jalapeno slices, and/or queso fresco. Serve right away.
Notes
You don't have to use both zucchini and yellow squash. You can use either.
Adding other vegetables such as corn, broccoli, and spinach is a great idea.
If you don't have black beans on hand, you are more than welcome to use other types of beans such as pinto and kidney beans.
You will need 5 to 6 tortillas depending on how thick you roll your enchilada. I tend to roll mine thick so I only ended up using 5. Also, I have used whole wheat and corn tortillas for these enchiladas and they tasted great!