Heat oil in a saute pan over a moderate flame. Add onion and garlic and cook, stirring frequently, until they begin to turn brown, about 5 minutes. Add pepper and cook 3 to 5 minutes. Add squash and chicken broth; bring to a boil, then lower heat and simmer until squash is almost tender, but not soft, about 10 minutes. Add frozen corn and peas, then add cream and thyme. Simmer 5 minutes, add salt and pepper to taste, and serve.