Heat 1/2 T oil in a large Dutch oven over med-high heat. Add half of the steak and cook, stirring occasionally, until browned, about 6 minutes. Remove steak from pan. Repeat.
Add; cook, stirring occasionally, until onion is tender, about 6 minutes.
Add. Cook 1 min stirring constantly.
Add; bring to a boil. Return steak to pan; cover, reduce heat to low, and simmer 30 minutes.
Stir in bell peppers; cook until steak is tender, about 30 minutes. Ladle chili into bowls; top with avocado, yogurt, scallions, cilantro, and, if desired, radishes.