Brown ground meat in skillet or Dutch Oven with onion and garlic, until all the pink is gone. Add taco seasoning and blend in well.
Stir in tomatoes, beans and salsa and mix until heated through. If you used a skillet, transfer meat mixture to a casserole dish and set aside. If you used a Dutch oven, set aside.
In a skillet (you can use the same skillet as meat mixture, just wipe it out with a paper towel), crumble the polenta and add chicken broth. Stir over medium heat until polenta begins to soften and look like mush. Add water gradually, until the consistency is that of mush - not too runny.
Stir in the corn and diced red pepper. Add salt and pepper to taste.
Spoon the polenta carefully over the meat mixture - either in the Dutch oven or the casserole dish.
Sprinkle cheese on top and bake at 350° for 20-30 min. Make sure to not cook too long, so polenta won't dry out.
Garnish with slice avocado, if desired.