Preheat oven to 350 F.
While in oven in preheating, start preparing enchilada sauce.
In a medium sauce pan, add olive oil and red onion (leave about 1/4 cup on side) & saute until translucent.
Then add in cumin, basil, oregano, garlic powder, red pepper flakes and stir until combined well.
Add tomato sauce, vegetarian broth, flour and salt + pepper to taste.
Leave it on low to simmer for 10 minutes.
Spread 1 cup of enchilada sauce on the bottom of the glass pyrex baking dish (~9×13).
To make the enchiladas, add chicken, zucchini + mushrooms & sprinkle of cheddar cheese in a tortilla.
Roll them up and do the same with the remaining of the tortillas.
Pour the rest of enchilada sauce when enchiladas are all assembled.
Sprinkle cheese & extra raw onions on top.
Cover baking dish with foil and bake for 25 minutes.
After 25 minutes, remove foil & bake for another 5 minutes.
Remove from oven & cool for 5 minutes before serving.
Garnish with cilantro & grape tomatoes. Add avocado if desired!