Heat oil in large saucepan over medium-high heat. Add 1 1/2 cups onions and next 3 ingredients. Sauté until beef is cooked through, breaking up with spoon, about 5 minutes. Add beans with liquid and tomatoes.
Simmer until thickened, about 15 minutes. Mix in cilantro, salt, and pepper.
Place sourdough toasts on plates. Top with chili, cheese, and remaining chopped red onions.