Heat EVOO in large skillet over medium heat; add onion and cook until soft, 5 minutes. Add peppers and cook for 15 minutes; season.
Whisk 3/4 tsp. salt and polenta into 3 cups boiling water. Lower heat and whisk until thickened, about 2 minutes. Whisk in 2 tbsp. butter and cream. Top with peppers, onion and remaining 1 tbsp. butter.