In a large pot over medium heat, brown the turkey. Add onions and garlic; saute for 1-2 minutes. Add diced tomatoes. Drain corn, drain and rinse beans. Add to the pot. Stir to combine, then add the chili powder, mixing well. Heat until bubbly, stirring occasionally.
Serve chili topped with sliced green onions and shredded cheese, with blackberries on the side.