In a very large skillet over medium heat add the oil. Once the oil is hot add the onion and cook until translucent. Add the bell peppers, zucchini, carrot, thyme, parsley and season with salt and pepper.
Cook for 5 minutes and add the fresh tomatoes.
Cook for another 3 minutes. Remove the vegetables from the skillet and place in a bowl. Do not clean the skillet.
Place the skillet over the heat over high and add the flat iron steak cubes. Sauté for 3 to 5 minutes. When all sides are golden brown, remove from the skillet and place in the same bowl of the vegetables.
Add the San Marzano tomatoes to the skillet and cook at medium heat for 5 minutes.
Return the vegetables and meat to the skillet with the tomatoes sauce. Season with salt and pepper.
Cook for 20 minutes making sure that the sauce will not dry out.
Prepare the Polenta according to the box directions. When done add the butter and mix well.
Place a nice mound of polenta in a bowl and cover with the tomatoes-vegetables sauce.