Bring vegetable stock to a boil over high heat. Reduce heat to medium and add salt, cilantro, and grapeseed oil. Whisking continuously, pour in polenta and continue whisking until smooth and thick (about 4-7 minutes). Pour polenta into an 11x14 jelly roll pan sprayed with cooking spray. Spread evenly into pan. Place in refrigerator for about 30 minutes or until firm.
Brown ground beef (or ground turkey or ground chicken). Add taco seasoning according to package directions.
Preheat oven to 350. Take polenta from refrigerator and bake for 40 minutes.
Remove crust from oven. Spread refried beans over crust. Layer browned ground beef (or ground turkey or ground chicken) over the top of the refried beans. Sprinkle with about 1/2 cup of the shredded cheese. Place back in the oven and bake for about 15-20 minutes.
Remove from oven. Top with lettuce, shredded cheese, tomatoes, onions, crushed tortilla chips and whatever other toppings you would like to add. Serve with taco sauce and sour cream.