Heat oil in a large Dutch oven over medium heat. Add sweet potato and turnip; sauté 5 minutes or until lightly browned. Add bell peppers, zucchini, and squash; sauté 3 minutes. Add mushrooms; sauté 1 minute. Add Corn Stock, Grilled Corn Kernels, hominy, thyme, sage, coriander seeds, and pepper. Combine water and cornstarch in a small bowl, stirring until well-blended; add to stew. Bring to a boil; reduce heat and simmer 5 minutes or until slightly thickened, stirring constantly.